Fix @Nullable for javalibs

Both VirtualMachine.load and VirtualMachineManager.get return
`null` when VM is not found.

Bug: n/a
Test: m
Change-Id: I5213bf7e103a35f210fdfb56f86e3de1afb56ae3
diff --git a/javalib/src/android/system/virtualmachine/VirtualMachine.java b/javalib/src/android/system/virtualmachine/VirtualMachine.java
index c48c4fe..14ff111 100644
--- a/javalib/src/android/system/virtualmachine/VirtualMachine.java
+++ b/javalib/src/android/system/virtualmachine/VirtualMachine.java
@@ -223,7 +223,7 @@
     }
 
     /** Loads a virtual machine that is already created before. */
-    /* package */ static @NonNull VirtualMachine load(
+    /* package */ static @Nullable VirtualMachine load(
             @NonNull Context context, @NonNull String name) throws VirtualMachineException {
         File configFilePath = getConfigFilePath(context, name);
         VirtualMachineConfig config;
diff --git a/javalib/src/android/system/virtualmachine/VirtualMachineManager.java b/javalib/src/android/system/virtualmachine/VirtualMachineManager.java
index 3654886..51fa51f 100644
--- a/javalib/src/android/system/virtualmachine/VirtualMachineManager.java
+++ b/javalib/src/android/system/virtualmachine/VirtualMachineManager.java
@@ -17,6 +17,7 @@
 package android.system.virtualmachine;
 
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.content.Context;
 
 import java.lang.ref.WeakReference;
@@ -72,7 +73,7 @@
      * Returns an existing {@link VirtualMachine} with the given name. Returns null if there is no
      * such virtual machine.
      */
-    public @NonNull VirtualMachine get(@NonNull String name) throws VirtualMachineException {
+    public @Nullable VirtualMachine get(@NonNull String name) throws VirtualMachineException {
         return VirtualMachine.load(mContext, name);
     }