diff --git a/services/core/java/com/android/server/net/NetworkStatsService.java b/services/core/java/com/android/server/net/NetworkStatsService.java
index f571b35..097b071 100644
--- a/services/core/java/com/android/server/net/NetworkStatsService.java
+++ b/services/core/java/com/android/server/net/NetworkStatsService.java
@@ -934,6 +934,11 @@
 
     @Override
     public String[] getMobileIfaces() {
+        // TODO (b/192758557): Remove debug log.
+        if (ArrayUtils.contains(mMobileIfaces, null)) {
+            throw new NullPointerException(
+                    "null element in mMobileIfaces: " + Arrays.toString(mMobileIfaces));
+        }
         return mMobileIfaces.clone();
     }
 
@@ -1383,6 +1388,11 @@
         }
 
         mMobileIfaces = mobileIfaces.toArray(new String[0]);
+        // TODO (b/192758557): Remove debug log.
+        if (ArrayUtils.contains(mMobileIfaces, null)) {
+            throw new NullPointerException(
+                    "null element in mMobileIfaces: " + Arrays.toString(mMobileIfaces));
+        }
     }
 
     private static int getSubIdForMobile(@NonNull NetworkStateSnapshot state) {