diff --git a/Tethering/apishim/30/com/android/networkstack/tethering/apishim/api30/BpfCoordinatorShimImpl.java b/Tethering/apishim/30/com/android/networkstack/tethering/apishim/api30/BpfCoordinatorShimImpl.java
index 22d2c5d..b865a8e 100644
--- a/Tethering/apishim/30/com/android/networkstack/tethering/apishim/api30/BpfCoordinatorShimImpl.java
+++ b/Tethering/apishim/30/com/android/networkstack/tethering/apishim/api30/BpfCoordinatorShimImpl.java
@@ -30,9 +30,9 @@
 import com.android.net.module.util.IBpfMap.ThrowingBiConsumer;
 import com.android.net.module.util.bpf.Tether4Key;
 import com.android.net.module.util.bpf.Tether4Value;
+import com.android.net.module.util.bpf.TetherStatsValue;
 import com.android.networkstack.tethering.BpfCoordinator.Dependencies;
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
-import com.android.networkstack.tethering.TetherStatsValue;
 
 /**
  * Bpf coordinator class for API shims.
diff --git a/Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java b/Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java
index 5afb862..0683e5e 100644
--- a/Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java
+++ b/Tethering/apishim/31/com/android/networkstack/tethering/apishim/api31/BpfCoordinatorShimImpl.java
@@ -33,6 +33,8 @@
 import com.android.net.module.util.IBpfMap.ThrowingBiConsumer;
 import com.android.net.module.util.bpf.Tether4Key;
 import com.android.net.module.util.bpf.Tether4Value;
+import com.android.net.module.util.bpf.TetherStatsKey;
+import com.android.net.module.util.bpf.TetherStatsValue;
 import com.android.networkstack.tethering.BpfCoordinator.Dependencies;
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
 import com.android.networkstack.tethering.BpfUtils;
@@ -42,8 +44,6 @@
 import com.android.networkstack.tethering.TetherDownstream6Key;
 import com.android.networkstack.tethering.TetherLimitKey;
 import com.android.networkstack.tethering.TetherLimitValue;
-import com.android.networkstack.tethering.TetherStatsKey;
-import com.android.networkstack.tethering.TetherStatsValue;
 import com.android.networkstack.tethering.TetherUpstream6Key;
 
 import java.io.FileDescriptor;
diff --git a/Tethering/apishim/common/com/android/networkstack/tethering/apishim/common/BpfCoordinatorShim.java b/Tethering/apishim/common/com/android/networkstack/tethering/apishim/common/BpfCoordinatorShim.java
index 915e210..69cbab5 100644
--- a/Tethering/apishim/common/com/android/networkstack/tethering/apishim/common/BpfCoordinatorShim.java
+++ b/Tethering/apishim/common/com/android/networkstack/tethering/apishim/common/BpfCoordinatorShim.java
@@ -25,9 +25,9 @@
 import com.android.net.module.util.IBpfMap.ThrowingBiConsumer;
 import com.android.net.module.util.bpf.Tether4Key;
 import com.android.net.module.util.bpf.Tether4Value;
+import com.android.net.module.util.bpf.TetherStatsValue;
 import com.android.networkstack.tethering.BpfCoordinator.Dependencies;
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
-import com.android.networkstack.tethering.TetherStatsValue;
 
 /**
  * Bpf coordinator class for API shims.
diff --git a/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java b/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
index f8a1094..bba0a40 100644
--- a/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
+++ b/Tethering/src/com/android/networkstack/tethering/BpfCoordinator.java
@@ -68,6 +68,8 @@
 import com.android.net.module.util.Struct.U32;
 import com.android.net.module.util.bpf.Tether4Key;
 import com.android.net.module.util.bpf.Tether4Value;
+import com.android.net.module.util.bpf.TetherStatsKey;
+import com.android.net.module.util.bpf.TetherStatsValue;
 import com.android.net.module.util.netlink.ConntrackMessage;
 import com.android.net.module.util.netlink.NetlinkConstants;
 import com.android.net.module.util.netlink.NetlinkSocket;
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherStatsKey.java b/Tethering/src/com/android/networkstack/tethering/TetherStatsKey.java
deleted file mode 100644
index 5442480..0000000
--- a/Tethering/src/com/android/networkstack/tethering/TetherStatsKey.java
+++ /dev/null
@@ -1,53 +0,0 @@
-/*
- * Copyright (C) 2020 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.android.networkstack.tethering;
-
-import com.android.net.module.util.Struct;
-import com.android.net.module.util.Struct.Field;
-import com.android.net.module.util.Struct.Type;
-
-/** The key of BpfMap which is used for tethering stats. */
-public class TetherStatsKey extends Struct {
-    @Field(order = 0, type = Type.U32)
-    public final long ifindex;  // upstream interface index
-
-    public TetherStatsKey(final long ifindex) {
-        this.ifindex = ifindex;
-    }
-
-    // TODO: remove equals, hashCode and toString once aosp/1536721 is merged.
-    @Override
-    public boolean equals(Object obj) {
-        if (this == obj) return true;
-
-        if (!(obj instanceof TetherStatsKey)) return false;
-
-        final TetherStatsKey that = (TetherStatsKey) obj;
-
-        return ifindex == that.ifindex;
-    }
-
-    @Override
-    public int hashCode() {
-        return Long.hashCode(ifindex);
-    }
-
-    @Override
-    public String toString() {
-        return String.format("ifindex: %d", ifindex);
-    }
-}
diff --git a/Tethering/src/com/android/networkstack/tethering/TetherStatsValue.java b/Tethering/src/com/android/networkstack/tethering/TetherStatsValue.java
deleted file mode 100644
index 844d2e8..0000000
--- a/Tethering/src/com/android/networkstack/tethering/TetherStatsValue.java
+++ /dev/null
@@ -1,80 +0,0 @@
-/*
- * Copyright (C) 2020 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package com.android.networkstack.tethering;
-
-import com.android.net.module.util.Struct;
-import com.android.net.module.util.Struct.Field;
-import com.android.net.module.util.Struct.Type;
-
-/** The key of BpfMap which is used for tethering stats. */
-public class TetherStatsValue extends Struct {
-    // Use the signed long variable to store the uint64 stats from stats BPF map.
-    // U63 is enough for each data element even at 5Gbps for ~468 years.
-    // 2^63 / (5 * 1000 * 1000 * 1000) * 8 / 86400 / 365 = 468.
-    @Field(order = 0, type = Type.U63)
-    public final long rxPackets;
-    @Field(order = 1, type = Type.U63)
-    public final long rxBytes;
-    @Field(order = 2, type = Type.U63)
-    public final long rxErrors;
-    @Field(order = 3, type = Type.U63)
-    public final long txPackets;
-    @Field(order = 4, type = Type.U63)
-    public final long txBytes;
-    @Field(order = 5, type = Type.U63)
-    public final long txErrors;
-
-    public TetherStatsValue(final long rxPackets, final long rxBytes, final long rxErrors,
-            final long txPackets, final long txBytes, final long txErrors) {
-        this.rxPackets = rxPackets;
-        this.rxBytes = rxBytes;
-        this.rxErrors = rxErrors;
-        this.txPackets = txPackets;
-        this.txBytes = txBytes;
-        this.txErrors = txErrors;
-    }
-
-    // TODO: remove equals, hashCode and toString once aosp/1536721 is merged.
-    @Override
-    public boolean equals(Object obj) {
-        if (this == obj) return true;
-
-        if (!(obj instanceof TetherStatsValue)) return false;
-
-        final TetherStatsValue that = (TetherStatsValue) obj;
-
-        return rxPackets == that.rxPackets
-                && rxBytes == that.rxBytes
-                && rxErrors == that.rxErrors
-                && txPackets == that.txPackets
-                && txBytes == that.txBytes
-                && txErrors == that.txErrors;
-    }
-
-    @Override
-    public int hashCode() {
-        return Long.hashCode(rxPackets) ^ Long.hashCode(rxBytes) ^ Long.hashCode(rxErrors)
-                ^ Long.hashCode(txPackets) ^ Long.hashCode(txBytes) ^ Long.hashCode(txErrors);
-    }
-
-    @Override
-    public String toString() {
-        return String.format("rxPackets: %s, rxBytes: %s, rxErrors: %s, txPackets: %s, "
-                + "txBytes: %s, txErrors: %s", rxPackets, rxBytes, rxErrors, txPackets,
-                txBytes, txErrors);
-    }
-}
diff --git a/Tethering/src/com/android/networkstack/tethering/util/TetheringUtils.java b/Tethering/src/com/android/networkstack/tethering/util/TetheringUtils.java
index 66d67a1..e6236df 100644
--- a/Tethering/src/com/android/networkstack/tethering/util/TetheringUtils.java
+++ b/Tethering/src/com/android/networkstack/tethering/util/TetheringUtils.java
@@ -22,7 +22,7 @@
 import androidx.annotation.NonNull;
 
 import com.android.net.module.util.JniUtil;
-import com.android.networkstack.tethering.TetherStatsValue;
+import com.android.net.module.util.bpf.TetherStatsValue;
 
 import java.io.FileDescriptor;
 import java.net.Inet6Address;
diff --git a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
index 43f1eaa..aac531a 100644
--- a/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
+++ b/Tethering/tests/unit/src/android/net/ip/IpServerTest.java
@@ -103,6 +103,8 @@
 import com.android.net.module.util.NetworkStackConstants;
 import com.android.net.module.util.bpf.Tether4Key;
 import com.android.net.module.util.bpf.Tether4Value;
+import com.android.net.module.util.bpf.TetherStatsKey;
+import com.android.net.module.util.bpf.TetherStatsValue;
 import com.android.networkstack.tethering.BpfCoordinator;
 import com.android.networkstack.tethering.BpfCoordinator.Ipv6ForwardingRule;
 import com.android.networkstack.tethering.PrivateAddressCoordinator;
@@ -112,8 +114,6 @@
 import com.android.networkstack.tethering.TetherDownstream6Key;
 import com.android.networkstack.tethering.TetherLimitKey;
 import com.android.networkstack.tethering.TetherLimitValue;
-import com.android.networkstack.tethering.TetherStatsKey;
-import com.android.networkstack.tethering.TetherStatsValue;
 import com.android.networkstack.tethering.TetherUpstream6Key;
 import com.android.networkstack.tethering.TetheringConfiguration;
 import com.android.networkstack.tethering.util.InterfaceSet;
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java
index 4967d27..3630f24 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/BpfCoordinatorTest.java
@@ -102,6 +102,8 @@
 import com.android.net.module.util.NetworkStackConstants;
 import com.android.net.module.util.bpf.Tether4Key;
 import com.android.net.module.util.bpf.Tether4Value;
+import com.android.net.module.util.bpf.TetherStatsKey;
+import com.android.net.module.util.bpf.TetherStatsValue;
 import com.android.net.module.util.netlink.ConntrackMessage;
 import com.android.net.module.util.netlink.NetlinkConstants;
 import com.android.net.module.util.netlink.NetlinkSocket;
diff --git a/framework-t/api/current.txt b/framework-t/api/current.txt
index 1b47481..eb77288 100644
--- a/framework-t/api/current.txt
+++ b/framework-t/api/current.txt
@@ -3,7 +3,7 @@
 
   public final class NetworkStats implements java.lang.AutoCloseable {
     method public void close();
-    method public boolean getNextBucket(android.app.usage.NetworkStats.Bucket);
+    method public boolean getNextBucket(@Nullable android.app.usage.NetworkStats.Bucket);
     method public boolean hasNextBucket();
   }
 
@@ -40,21 +40,21 @@
   }
 
   public class NetworkStatsManager {
-    method @WorkerThread public android.app.usage.NetworkStats queryDetails(int, String, long, long) throws android.os.RemoteException, java.lang.SecurityException;
-    method @WorkerThread public android.app.usage.NetworkStats queryDetailsForUid(int, String, long, long, int) throws java.lang.SecurityException;
-    method @WorkerThread public android.app.usage.NetworkStats queryDetailsForUidTag(int, String, long, long, int, int) throws java.lang.SecurityException;
-    method @WorkerThread public android.app.usage.NetworkStats queryDetailsForUidTagState(int, String, long, long, int, int, int) throws java.lang.SecurityException;
-    method @WorkerThread public android.app.usage.NetworkStats querySummary(int, String, long, long) throws android.os.RemoteException, java.lang.SecurityException;
-    method @WorkerThread public android.app.usage.NetworkStats.Bucket querySummaryForDevice(int, String, long, long) throws android.os.RemoteException, java.lang.SecurityException;
-    method @WorkerThread public android.app.usage.NetworkStats.Bucket querySummaryForUser(int, String, long, long) throws android.os.RemoteException, java.lang.SecurityException;
-    method public void registerUsageCallback(int, String, long, android.app.usage.NetworkStatsManager.UsageCallback);
-    method public void registerUsageCallback(int, String, long, android.app.usage.NetworkStatsManager.UsageCallback, @Nullable android.os.Handler);
-    method public void unregisterUsageCallback(android.app.usage.NetworkStatsManager.UsageCallback);
+    method @WorkerThread public android.app.usage.NetworkStats queryDetails(int, @Nullable String, long, long) throws android.os.RemoteException, java.lang.SecurityException;
+    method @NonNull @WorkerThread public android.app.usage.NetworkStats queryDetailsForUid(int, @Nullable String, long, long, int) throws java.lang.SecurityException;
+    method @NonNull @WorkerThread public android.app.usage.NetworkStats queryDetailsForUidTag(int, @Nullable String, long, long, int, int) throws java.lang.SecurityException;
+    method @NonNull @WorkerThread public android.app.usage.NetworkStats queryDetailsForUidTagState(int, @Nullable String, long, long, int, int, int) throws java.lang.SecurityException;
+    method @WorkerThread public android.app.usage.NetworkStats querySummary(int, @Nullable String, long, long) throws android.os.RemoteException, java.lang.SecurityException;
+    method @WorkerThread public android.app.usage.NetworkStats.Bucket querySummaryForDevice(int, @Nullable String, long, long) throws android.os.RemoteException, java.lang.SecurityException;
+    method @WorkerThread public android.app.usage.NetworkStats.Bucket querySummaryForUser(int, @Nullable String, long, long) throws android.os.RemoteException, java.lang.SecurityException;
+    method public void registerUsageCallback(int, @Nullable String, long, @NonNull android.app.usage.NetworkStatsManager.UsageCallback);
+    method public void registerUsageCallback(int, @Nullable String, long, @NonNull android.app.usage.NetworkStatsManager.UsageCallback, @Nullable android.os.Handler);
+    method public void unregisterUsageCallback(@NonNull android.app.usage.NetworkStatsManager.UsageCallback);
   }
 
   public abstract static class NetworkStatsManager.UsageCallback {
     ctor public NetworkStatsManager.UsageCallback();
-    method public abstract void onThresholdReached(int, String);
+    method public abstract void onThresholdReached(int, @Nullable String);
   }
 
 }
@@ -173,12 +173,12 @@
     method public static void incrementOperationCount(int, int);
     method public static void setThreadStatsTag(int);
     method public static void setThreadStatsUid(int);
-    method public static void tagDatagramSocket(java.net.DatagramSocket) throws java.net.SocketException;
-    method public static void tagFileDescriptor(java.io.FileDescriptor) throws java.io.IOException;
-    method public static void tagSocket(java.net.Socket) throws java.net.SocketException;
-    method public static void untagDatagramSocket(java.net.DatagramSocket) throws java.net.SocketException;
-    method public static void untagFileDescriptor(java.io.FileDescriptor) throws java.io.IOException;
-    method public static void untagSocket(java.net.Socket) throws java.net.SocketException;
+    method public static void tagDatagramSocket(@NonNull java.net.DatagramSocket) throws java.net.SocketException;
+    method public static void tagFileDescriptor(@NonNull java.io.FileDescriptor) throws java.io.IOException;
+    method public static void tagSocket(@NonNull java.net.Socket) throws java.net.SocketException;
+    method public static void untagDatagramSocket(@NonNull java.net.DatagramSocket) throws java.net.SocketException;
+    method public static void untagFileDescriptor(@NonNull java.io.FileDescriptor) throws java.io.IOException;
+    method public static void untagSocket(@NonNull java.net.Socket) throws java.net.SocketException;
     field public static final int UNSUPPORTED = -1; // 0xffffffff
   }
 
diff --git a/framework-t/api/lint-baseline.txt b/framework-t/api/lint-baseline.txt
index 53e1beb..2996a3e 100644
--- a/framework-t/api/lint-baseline.txt
+++ b/framework-t/api/lint-baseline.txt
@@ -41,86 +41,18 @@
     android.net.IpSecTransform.Builder does not declare a `build()` method, but builder classes are expected to
 
 
-MissingNullability: android.app.usage.NetworkStats#getNextBucket(android.app.usage.NetworkStats.Bucket) parameter #0:
-    Missing nullability on parameter `bucketOut` in method `getNextBucket`
 MissingNullability: android.app.usage.NetworkStatsManager#queryDetails(int, String, long, long):
     Missing nullability on method `queryDetails` return
-MissingNullability: android.app.usage.NetworkStatsManager#queryDetails(int, String, long, long) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `queryDetails`
-MissingNullability: android.app.usage.NetworkStatsManager#queryDetailsForUid(int, String, long, long, int):
-    Missing nullability on method `queryDetailsForUid` return
-MissingNullability: android.app.usage.NetworkStatsManager#queryDetailsForUid(int, String, long, long, int) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `queryDetailsForUid`
-MissingNullability: android.app.usage.NetworkStatsManager#queryDetailsForUidTag(int, String, long, long, int, int):
-    Missing nullability on method `queryDetailsForUidTag` return
-MissingNullability: android.app.usage.NetworkStatsManager#queryDetailsForUidTag(int, String, long, long, int, int) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `queryDetailsForUidTag`
-MissingNullability: android.app.usage.NetworkStatsManager#queryDetailsForUidTagState(int, String, long, long, int, int, int):
-    Missing nullability on method `queryDetailsForUidTagState` return
-MissingNullability: android.app.usage.NetworkStatsManager#queryDetailsForUidTagState(int, String, long, long, int, int, int) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `queryDetailsForUidTagState`
 MissingNullability: android.app.usage.NetworkStatsManager#querySummary(int, String, long, long):
     Missing nullability on method `querySummary` return
-MissingNullability: android.app.usage.NetworkStatsManager#querySummary(int, String, long, long) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `querySummary`
 MissingNullability: android.app.usage.NetworkStatsManager#querySummaryForDevice(int, String, long, long):
     Missing nullability on method `querySummaryForDevice` return
-MissingNullability: android.app.usage.NetworkStatsManager#querySummaryForDevice(int, String, long, long) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `querySummaryForDevice`
 MissingNullability: android.app.usage.NetworkStatsManager#querySummaryForUser(int, String, long, long):
     Missing nullability on method `querySummaryForUser` return
-MissingNullability: android.app.usage.NetworkStatsManager#querySummaryForUser(int, String, long, long) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `querySummaryForUser`
-MissingNullability: android.app.usage.NetworkStatsManager#registerUsageCallback(int, String, long, android.app.usage.NetworkStatsManager.UsageCallback) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `registerUsageCallback`
-MissingNullability: android.app.usage.NetworkStatsManager#registerUsageCallback(int, String, long, android.app.usage.NetworkStatsManager.UsageCallback) parameter #3:
-    Missing nullability on parameter `callback` in method `registerUsageCallback`
-MissingNullability: android.app.usage.NetworkStatsManager#registerUsageCallback(int, String, long, android.app.usage.NetworkStatsManager.UsageCallback, android.os.Handler) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `registerUsageCallback`
-MissingNullability: android.app.usage.NetworkStatsManager#registerUsageCallback(int, String, long, android.app.usage.NetworkStatsManager.UsageCallback, android.os.Handler) parameter #3:
-    Missing nullability on parameter `callback` in method `registerUsageCallback`
-MissingNullability: android.app.usage.NetworkStatsManager#unregisterUsageCallback(android.app.usage.NetworkStatsManager.UsageCallback) parameter #0:
-    Missing nullability on parameter `callback` in method `unregisterUsageCallback`
-MissingNullability: android.app.usage.NetworkStatsManager.UsageCallback#onThresholdReached(int, String) parameter #1:
-    Missing nullability on parameter `subscriberId` in method `onThresholdReached`
 MissingNullability: android.net.IpSecAlgorithm#writeToParcel(android.os.Parcel, int) parameter #0:
     Missing nullability on parameter `out` in method `writeToParcel`
 MissingNullability: android.net.IpSecManager.UdpEncapsulationSocket#getFileDescriptor():
     Missing nullability on method `getFileDescriptor` return
-MissingNullability: android.net.TrafficStats#tagDatagramSocket(java.net.DatagramSocket) parameter #0:
-    Missing nullability on parameter `socket` in method `tagDatagramSocket`
-MissingNullability: android.net.TrafficStats#tagFileDescriptor(java.io.FileDescriptor) parameter #0:
-    Missing nullability on parameter `fd` in method `tagFileDescriptor`
-MissingNullability: android.net.TrafficStats#tagSocket(java.net.Socket) parameter #0:
-    Missing nullability on parameter `socket` in method `tagSocket`
-MissingNullability: android.net.TrafficStats#untagDatagramSocket(java.net.DatagramSocket) parameter #0:
-    Missing nullability on parameter `socket` in method `untagDatagramSocket`
-MissingNullability: android.net.TrafficStats#untagFileDescriptor(java.io.FileDescriptor) parameter #0:
-    Missing nullability on parameter `fd` in method `untagFileDescriptor`
-MissingNullability: android.net.TrafficStats#untagSocket(java.net.Socket) parameter #0:
-    Missing nullability on parameter `socket` in method `untagSocket`
-MissingNullability: com.android.internal.util.FileRotator#FileRotator(java.io.File, String, long, long) parameter #0:
-    Missing nullability on parameter `basePath` in method `FileRotator`
-MissingNullability: com.android.internal.util.FileRotator#FileRotator(java.io.File, String, long, long) parameter #1:
-    Missing nullability on parameter `prefix` in method `FileRotator`
-MissingNullability: com.android.internal.util.FileRotator#dumpAll(java.io.OutputStream) parameter #0:
-    Missing nullability on parameter `os` in method `dumpAll`
-MissingNullability: com.android.internal.util.FileRotator#readMatching(com.android.internal.util.FileRotator.Reader, long, long) parameter #0:
-    Missing nullability on parameter `reader` in method `readMatching`
-MissingNullability: com.android.internal.util.FileRotator#rewriteActive(com.android.internal.util.FileRotator.Rewriter, long) parameter #0:
-    Missing nullability on parameter `rewriter` in method `rewriteActive`
-MissingNullability: com.android.internal.util.FileRotator#rewriteAll(com.android.internal.util.FileRotator.Rewriter) parameter #0:
-    Missing nullability on parameter `rewriter` in method `rewriteAll`
-MissingNullability: com.android.internal.util.FileRotator.Reader#read(java.io.InputStream) parameter #0:
-    Missing nullability on parameter `in` in method `read`
-MissingNullability: com.android.internal.util.FileRotator.Writer#write(java.io.OutputStream) parameter #0:
-    Missing nullability on parameter `out` in method `write`
-MissingNullability: com.android.server.NetworkManagementSocketTagger#kernelToTag(String) parameter #0:
-    Missing nullability on parameter `string` in method `kernelToTag`
-MissingNullability: com.android.server.NetworkManagementSocketTagger#tag(java.io.FileDescriptor) parameter #0:
-    Missing nullability on parameter `fd` in method `tag`
-MissingNullability: com.android.server.NetworkManagementSocketTagger#untag(java.io.FileDescriptor) parameter #0:
-    Missing nullability on parameter `fd` in method `untag`
 
 
 RethrowRemoteException: android.app.usage.NetworkStatsManager#queryDetails(int, String, long, long):
diff --git a/framework-t/api/module-lib-current.txt b/framework-t/api/module-lib-current.txt
index 658c625..c1f7b39 100644
--- a/framework-t/api/module-lib-current.txt
+++ b/framework-t/api/module-lib-current.txt
@@ -4,6 +4,8 @@
   public class NetworkStatsManager {
     method @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK}) public void forceUpdate();
     method public static int getCollapsedRatType(int);
+    method @NonNull @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK}) public android.net.NetworkStats getMobileUidStats();
+    method @NonNull @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK}) public android.net.NetworkStats getWifiUidStats();
     method @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK}) public void noteUidForeground(int, boolean);
     method @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK}) public void notifyNetworkStatus(@NonNull java.util.List<android.net.Network>, @NonNull java.util.List<android.net.NetworkStateSnapshot>, @Nullable String, @NonNull java.util.List<android.net.UnderlyingNetworkInfo>);
     method @NonNull @WorkerThread public android.app.usage.NetworkStats queryDetailsForDevice(@NonNull android.net.NetworkTemplate, long, long);
@@ -182,6 +184,7 @@
   public class TrafficStats {
     method public static void attachSocketTagger();
     method public static void init(@NonNull android.content.Context);
+    method public static void setThreadStatsTagDownload();
   }
 
   public final class UnderlyingNetworkInfo implements android.os.Parcelable {
diff --git a/framework-t/api/system-current.txt b/framework-t/api/system-current.txt
index 0f37b6f..6460fed 100644
--- a/framework-t/api/system-current.txt
+++ b/framework-t/api/system-current.txt
@@ -2,10 +2,8 @@
 package android.app.usage {
 
   public class NetworkStatsManager {
-    method @NonNull @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK}) public android.net.NetworkStats getMobileUidStats();
-    method @NonNull @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK}) public android.net.NetworkStats getWifiUidStats();
-    method @NonNull @RequiresPermission(anyOf={android.Manifest.permission.NETWORK_STATS_PROVIDER, android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK}) public void registerNetworkStatsProvider(@NonNull String, @NonNull android.net.netstats.provider.NetworkStatsProvider);
-    method @NonNull @RequiresPermission(anyOf={android.Manifest.permission.NETWORK_STATS_PROVIDER, android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK}) public void unregisterNetworkStatsProvider(@NonNull android.net.netstats.provider.NetworkStatsProvider);
+    method @RequiresPermission(anyOf={android.Manifest.permission.NETWORK_STATS_PROVIDER, android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK}) public void registerNetworkStatsProvider(@NonNull String, @NonNull android.net.netstats.provider.NetworkStatsProvider);
+    method @RequiresPermission(anyOf={android.Manifest.permission.NETWORK_STATS_PROVIDER, android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK}) public void unregisterNetworkStatsProvider(@NonNull android.net.netstats.provider.NetworkStatsProvider);
   }
 
 }
@@ -113,7 +111,6 @@
   public class TrafficStats {
     method public static void setThreadStatsTagApp();
     method public static void setThreadStatsTagBackup();
-    method public static void setThreadStatsTagDownload();
     method public static void setThreadStatsTagRestore();
     field public static final int TAG_NETWORK_STACK_IMPERSONATION_RANGE_END = -113; // 0xffffff8f
     field public static final int TAG_NETWORK_STACK_IMPERSONATION_RANGE_START = -128; // 0xffffff80
diff --git a/framework-t/src/android/app/usage/NetworkStats.java b/framework-t/src/android/app/usage/NetworkStats.java
index 2b6570a..74fe4bd 100644
--- a/framework-t/src/android/app/usage/NetworkStats.java
+++ b/framework-t/src/android/app/usage/NetworkStats.java
@@ -17,6 +17,7 @@
 package android.app.usage;
 
 import android.annotation.IntDef;
+import android.annotation.Nullable;
 import android.content.Context;
 import android.net.INetworkStatsService;
 import android.net.INetworkStatsSession;
@@ -474,10 +475,11 @@
 
     /**
      * Fills the recycled bucket with data of the next bin in the enumeration.
-     * @param bucketOut Bucket to be filled with data.
+     * @param bucketOut Bucket to be filled with data. If null, the method does
+     *                  nothing and returning false.
      * @return true if successfully filled the bucket, false otherwise.
      */
-    public boolean getNextBucket(Bucket bucketOut) {
+    public boolean getNextBucket(@Nullable Bucket bucketOut) {
         if (mSummary != null) {
             return getNextSummaryBucket(bucketOut);
         } else {
@@ -651,7 +653,7 @@
      * @param bucketOut Next item will be set here.
      * @return true if a next item could be set.
      */
-    private boolean getNextSummaryBucket(Bucket bucketOut) {
+    private boolean getNextSummaryBucket(@Nullable Bucket bucketOut) {
         if (bucketOut != null && mEnumerationIndex < mSummary.size()) {
             mRecycledSummaryEntry = mSummary.getValues(mEnumerationIndex++, mRecycledSummaryEntry);
             fillBucketFromSummaryEntry(bucketOut);
@@ -678,7 +680,7 @@
      * @param bucketOut Next item will be set here.
      * @return true if a next item could be set.
      */
-    private boolean getNextHistoryBucket(Bucket bucketOut) {
+    private boolean getNextHistoryBucket(@Nullable Bucket bucketOut) {
         if (bucketOut != null && mHistory != null) {
             if (mEnumerationIndex < mHistory.size()) {
                 mRecycledHistoryEntry = mHistory.getValues(mEnumerationIndex++,
diff --git a/framework-t/src/android/app/usage/NetworkStatsManager.java b/framework-t/src/android/app/usage/NetworkStatsManager.java
index bf518b2..f41475b 100644
--- a/framework-t/src/android/app/usage/NetworkStatsManager.java
+++ b/framework-t/src/android/app/usage/NetworkStatsManager.java
@@ -290,7 +290,7 @@
      *         statistics collection.
      */
     @WorkerThread
-    public Bucket querySummaryForDevice(int networkType, String subscriberId,
+    public Bucket querySummaryForDevice(int networkType, @Nullable String subscriberId,
             long startTime, long endTime) throws SecurityException, RemoteException {
         NetworkTemplate template;
         try {
@@ -335,8 +335,8 @@
      *         statistics collection.
      */
     @WorkerThread
-    public Bucket querySummaryForUser(int networkType, String subscriberId, long startTime,
-            long endTime) throws SecurityException, RemoteException {
+    public Bucket querySummaryForUser(int networkType, @Nullable String subscriberId,
+            long startTime, long endTime) throws SecurityException, RemoteException {
         NetworkTemplate template;
         try {
             template = createTemplate(networkType, subscriberId);
@@ -384,7 +384,7 @@
      *         statistics collection.
      */
     @WorkerThread
-    public NetworkStats querySummary(int networkType, String subscriberId, long startTime,
+    public NetworkStats querySummary(int networkType, @Nullable String subscriberId, long startTime,
             long endTime) throws SecurityException, RemoteException {
         NetworkTemplate template;
         try {
@@ -508,15 +508,17 @@
      *
      * @see #queryDetailsForUidTagState(int, String, long, long, int, int, int)
      */
+    @NonNull
     @WorkerThread
-    public NetworkStats queryDetailsForUid(int networkType, String subscriberId,
+    public NetworkStats queryDetailsForUid(int networkType, @Nullable String subscriberId,
             long startTime, long endTime, int uid) throws SecurityException {
         return queryDetailsForUidTagState(networkType, subscriberId, startTime, endTime, uid,
             NetworkStats.Bucket.TAG_NONE, NetworkStats.Bucket.STATE_ALL);
     }
 
     /** @hide */
-    public NetworkStats queryDetailsForUid(NetworkTemplate template,
+    @NonNull
+    public NetworkStats queryDetailsForUid(@NonNull NetworkTemplate template,
             long startTime, long endTime, int uid) throws SecurityException {
         return queryDetailsForUidTagState(template, startTime, endTime, uid,
                 NetworkStats.Bucket.TAG_NONE, NetworkStats.Bucket.STATE_ALL);
@@ -524,23 +526,59 @@
 
     /**
      * Query network usage statistics details for a given uid and tag.
+     *
+     * This may take a long time, and apps should avoid calling this on their main thread.
+     * Only usable for uids belonging to calling user. Result is not aggregated over time.
+     * This means buckets' start and end timestamps are going to be between 'startTime' and
+     * 'endTime' parameters. The uid is going to be the same as the 'uid' parameter, the tag
+     * the same as the 'tag' parameter, and the state the same as the 'state' parameter.
+     * defaultNetwork is going to be {@link NetworkStats.Bucket#DEFAULT_NETWORK_ALL},
+     * metered is going to be {@link NetworkStats.Bucket#METERED_ALL}, and
+     * roaming is going to be {@link NetworkStats.Bucket#ROAMING_ALL}.
+     * <p>Only includes buckets that atomically occur in the inclusive time range. Doesn't
+     * interpolate across partial buckets. Since bucket length is in the order of hours, this
+     * method cannot be used to measure data usage on a fine grained time scale.
      * This may take a long time, and apps should avoid calling this on their main thread.
      *
-     * @see #queryDetailsForUidTagState(int, String, long, long, int, int, int)
+     * @param networkType As defined in {@link ConnectivityManager}, e.g.
+     *            {@link ConnectivityManager#TYPE_MOBILE}, {@link ConnectivityManager#TYPE_WIFI}
+     *            etc.
+     * @param subscriberId If applicable, the subscriber id of the network interface.
+     *                     <p>Starting with API level 29, the {@code subscriberId} is guarded by
+     *                     additional restrictions. Calling apps that do not meet the new
+     *                     requirements to access the {@code subscriberId} can provide a {@code
+     *                     null} value when querying for the mobile network type to receive usage
+     *                     for all mobile networks. For additional details see {@link
+     *                     TelephonyManager#getSubscriberId()}.
+     *                     <p>Starting with API level 31, calling apps can provide a
+     *                     {@code subscriberId} with wifi network type to receive usage for
+     *                     wifi networks which is under the given subscription if applicable.
+     *                     Otherwise, pass {@code null} when querying all wifi networks.
+     * @param startTime Start of period. Defined in terms of "Unix time", see
+     *            {@link java.lang.System#currentTimeMillis}.
+     * @param endTime End of period. Defined in terms of "Unix time", see
+     *            {@link java.lang.System#currentTimeMillis}.
+     * @param uid UID of app
+     * @param tag TAG of interest. Use {@link NetworkStats.Bucket#TAG_NONE} for aggregated data
+     *            across all the tags.
+     * @return Statistics which is described above.
+     * @throws SecurityException if permissions are insufficient to read network statistics.
      */
+    @NonNull
     @WorkerThread
-    public NetworkStats queryDetailsForUidTag(int networkType, String subscriberId,
+    public NetworkStats queryDetailsForUidTag(int networkType, @Nullable String subscriberId,
             long startTime, long endTime, int uid, int tag) throws SecurityException {
         return queryDetailsForUidTagState(networkType, subscriberId, startTime, endTime, uid,
             tag, NetworkStats.Bucket.STATE_ALL);
     }
 
     /**
-     * Query network usage statistics details for a given uid, tag, and state. Only usable for uids
-     * belonging to calling user. Result is not aggregated over time. This means buckets' start and
-     * end timestamps are going to be between 'startTime' and 'endTime' parameters. The uid is going
-     * to be the same as the 'uid' parameter, the tag the same as the 'tag' parameter, and the state
-     * the same as the 'state' parameter.
+     * Query network usage statistics details for a given uid, tag, and state.
+     *
+     * Only usable for uids belonging to calling user. Result is not aggregated over time.
+     * This means buckets' start and end timestamps are going to be between 'startTime' and
+     * 'endTime' parameters. The uid is going to be the same as the 'uid' parameter, the tag
+     * the same as the 'tag' parameter, and the state the same as the 'state' parameter.
      * defaultNetwork is going to be {@link NetworkStats.Bucket#DEFAULT_NETWORK_ALL},
      * metered is going to be {@link NetworkStats.Bucket#METERED_ALL}, and
      * roaming is going to be {@link NetworkStats.Bucket#ROAMING_ALL}.
@@ -572,11 +610,12 @@
      *            across all the tags.
      * @param state state of interest. Use {@link NetworkStats.Bucket#STATE_ALL} to aggregate
      *            traffic from all states.
-     * @return Statistics object or null if an error happened during statistics collection.
+     * @return Statistics which is described above.
      * @throws SecurityException if permissions are insufficient to read network statistics.
      */
+    @NonNull
     @WorkerThread
-    public NetworkStats queryDetailsForUidTagState(int networkType, String subscriberId,
+    public NetworkStats queryDetailsForUidTagState(int networkType, @Nullable String subscriberId,
             long startTime, long endTime, int uid, int tag, int state) throws SecurityException {
         NetworkTemplate template;
         template = createTemplate(networkType, subscriberId);
@@ -669,7 +708,7 @@
      *         statistics collection.
      */
     @WorkerThread
-    public NetworkStats queryDetails(int networkType, String subscriberId, long startTime,
+    public NetworkStats queryDetails(int networkType, @Nullable String subscriberId, long startTime,
             long endTime) throws SecurityException, RemoteException {
         NetworkTemplate template;
         try {
@@ -698,7 +737,7 @@
      *
      * @hide
      */
-    @SystemApi
+    @SystemApi(client = MODULE_LIBRARIES)
     @RequiresPermission(anyOf = {
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK,
             android.Manifest.permission.NETWORK_STACK})
@@ -724,7 +763,7 @@
      *
      * @hide
      */
-    @SystemApi
+    @SystemApi(client = MODULE_LIBRARIES)
     @RequiresPermission(anyOf = {
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK,
             android.Manifest.permission.NETWORK_STACK})
@@ -785,10 +824,28 @@
     /**
      * Registers to receive notifications about data usage on specified networks.
      *
-     * @see #registerUsageCallback(int, String, long, UsageCallback, Handler)
+     * <p>The callbacks will continue to be called as long as the process is live or
+     * {@link #unregisterUsageCallback} is called.
+     *
+     * @param networkType Type of network to monitor. Either
+    {@link ConnectivityManager#TYPE_MOBILE} or {@link ConnectivityManager#TYPE_WIFI}.
+     * @param subscriberId If applicable, the subscriber id of the network interface.
+     *                     <p>Starting with API level 29, the {@code subscriberId} is guarded by
+     *                     additional restrictions. Calling apps that do not meet the new
+     *                     requirements to access the {@code subscriberId} can provide a {@code
+     *                     null} value when registering for the mobile network type to receive
+     *                     notifications for all mobile networks. For additional details see {@link
+     *                     TelephonyManager#getSubscriberId()}.
+     *                     <p>Starting with API level 31, calling apps can provide a
+     *                     {@code subscriberId} with wifi network type to receive usage for
+     *                     wifi networks which is under the given subscription if applicable.
+     *                     Otherwise, pass {@code null} when querying all wifi networks.
+     * @param thresholdBytes Threshold in bytes to be notified on.
+     * @param callback The {@link UsageCallback} that the system will call when data usage
+     *            has exceeded the specified threshold.
      */
-    public void registerUsageCallback(int networkType, String subscriberId, long thresholdBytes,
-            UsageCallback callback) {
+    public void registerUsageCallback(int networkType, @Nullable String subscriberId,
+            long thresholdBytes, @NonNull UsageCallback callback) {
         registerUsageCallback(networkType, subscriberId, thresholdBytes, callback,
                 null /* handler */);
     }
@@ -818,8 +875,8 @@
      * @param handler to dispatch callback events through, otherwise if {@code null} it uses
      *            the calling thread.
      */
-    public void registerUsageCallback(int networkType, String subscriberId, long thresholdBytes,
-            UsageCallback callback, @Nullable Handler handler) {
+    public void registerUsageCallback(int networkType, @Nullable String subscriberId,
+            long thresholdBytes, @NonNull UsageCallback callback, @Nullable Handler handler) {
         NetworkTemplate template = createTemplate(networkType, subscriberId);
         if (DBG) {
             Log.d(TAG, "registerUsageCallback called with: {"
@@ -839,7 +896,7 @@
      *
      * @param callback The {@link UsageCallback} used when registering.
      */
-    public void unregisterUsageCallback(UsageCallback callback) {
+    public void unregisterUsageCallback(@NonNull UsageCallback callback) {
         if (callback == null || callback.request == null
                 || callback.request.requestId == DataUsageRequest.REQUEST_ID_UNSET) {
             throw new IllegalArgumentException("Invalid UsageCallback");
@@ -880,7 +937,7 @@
         /**
          * Called when data usage has reached the given threshold.
          */
-        public abstract void onThresholdReached(int networkType, String subscriberId);
+        public abstract void onThresholdReached(int networkType, @Nullable String subscriberId);
 
         /**
          * @hide used for internal bookkeeping
@@ -924,7 +981,7 @@
     @RequiresPermission(anyOf = {
             android.Manifest.permission.NETWORK_STATS_PROVIDER,
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK})
-    @NonNull public void registerNetworkStatsProvider(
+    public void registerNetworkStatsProvider(
             @NonNull String tag,
             @NonNull NetworkStatsProvider provider) {
         try {
@@ -950,7 +1007,7 @@
     @RequiresPermission(anyOf = {
             android.Manifest.permission.NETWORK_STATS_PROVIDER,
             NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK})
-    @NonNull public void unregisterNetworkStatsProvider(@NonNull NetworkStatsProvider provider) {
+    public void unregisterNetworkStatsProvider(@NonNull NetworkStatsProvider provider) {
         try {
             provider.getProviderCallbackBinderOrThrow().unregister();
         } catch (RemoteException e) {
@@ -958,7 +1015,7 @@
         }
     }
 
-    private static NetworkTemplate createTemplate(int networkType, String subscriberId) {
+    private static NetworkTemplate createTemplate(int networkType, @Nullable String subscriberId) {
         final NetworkTemplate template;
         switch (networkType) {
             case ConnectivityManager.TYPE_MOBILE:
diff --git a/framework-t/src/android/net/NetworkStats.java b/framework-t/src/android/net/NetworkStats.java
index 06f2a62..51ff5ec 100644
--- a/framework-t/src/android/net/NetworkStats.java
+++ b/framework-t/src/android/net/NetworkStats.java
@@ -124,7 +124,6 @@
     public @Nullable static final String[] INTERFACES_ALL = null;
 
     /** {@link #tag} value for total data across all tags. */
-    // TODO: Rename TAG_NONE to TAG_ALL.
     public static final int TAG_NONE = 0;
 
     /** {@link #metered} value to account for all metered states. */
@@ -412,21 +411,24 @@
         /**
          * @return the metered state.
          */
-        @Meteredness public int getMetered() {
+        @Meteredness
+        public int getMetered() {
             return metered;
         }
 
         /**
          * @return the roaming state.
          */
-        @Roaming public int getRoaming() {
+        @Roaming
+        public int getRoaming() {
             return roaming;
         }
 
         /**
          * @return the default network state.
          */
-        @DefaultNetwork public int getDefaultNetwork() {
+        @DefaultNetwork
+        public int getDefaultNetwork() {
             return defaultNetwork;
         }
 
diff --git a/framework-t/src/android/net/TrafficStats.java b/framework-t/src/android/net/TrafficStats.java
index bc836d8..dc4ac55 100644
--- a/framework-t/src/android/net/TrafficStats.java
+++ b/framework-t/src/android/net/TrafficStats.java
@@ -205,7 +205,7 @@
      *                server context.
      * @hide
      */
-    @SystemApi(client = SystemApi.Client.MODULE_LIBRARIES)
+    @SystemApi(client = MODULE_LIBRARIES)
     @SuppressLint("VisiblySynchronized")
     public static synchronized void init(@NonNull final Context context) {
         if (sStatsService != null) {
@@ -376,7 +376,7 @@
      *
      * @hide
      */
-    @SystemApi
+    @SystemApi(client = MODULE_LIBRARIES)
     public static void setThreadStatsTagDownload() {
         setThreadStatsTag(TAG_SYSTEM_DOWNLOAD);
     }
@@ -468,7 +468,7 @@
      *
      * @see #setThreadStatsTag(int)
      */
-    public static void tagSocket(Socket socket) throws SocketException {
+    public static void tagSocket(@NonNull Socket socket) throws SocketException {
         SocketTagger.get().tag(socket);
     }
 
@@ -483,7 +483,7 @@
      * calling {@code untagSocket()} before sending the socket to another
      * process.
      */
-    public static void untagSocket(Socket socket) throws SocketException {
+    public static void untagSocket(@NonNull Socket socket) throws SocketException {
         SocketTagger.get().untag(socket);
     }
 
@@ -496,14 +496,14 @@
      *
      * @see #setThreadStatsTag(int)
      */
-    public static void tagDatagramSocket(DatagramSocket socket) throws SocketException {
+    public static void tagDatagramSocket(@NonNull DatagramSocket socket) throws SocketException {
         SocketTagger.get().tag(socket);
     }
 
     /**
      * Remove any statistics parameters from the given {@link DatagramSocket}.
      */
-    public static void untagDatagramSocket(DatagramSocket socket) throws SocketException {
+    public static void untagDatagramSocket(@NonNull DatagramSocket socket) throws SocketException {
         SocketTagger.get().untag(socket);
     }
 
@@ -516,7 +516,7 @@
      *
      * @see #setThreadStatsTag(int)
      */
-    public static void tagFileDescriptor(FileDescriptor fd) throws IOException {
+    public static void tagFileDescriptor(@NonNull FileDescriptor fd) throws IOException {
         SocketTagger.get().tag(fd);
     }
 
@@ -524,7 +524,7 @@
      * Remove any statistics parameters from the given {@link FileDescriptor}
      * socket.
      */
-    public static void untagFileDescriptor(FileDescriptor fd) throws IOException {
+    public static void untagFileDescriptor(@NonNull FileDescriptor fd) throws IOException {
         SocketTagger.get().untag(fd);
     }