diff --git a/core/java/android/net/NetworkCapabilities.java b/core/java/android/net/NetworkCapabilities.java
index e1cfe99..99375f8 100644
--- a/core/java/android/net/NetworkCapabilities.java
+++ b/core/java/android/net/NetworkCapabilities.java
@@ -17,6 +17,7 @@
 package android.net;
 
 import android.annotation.IntDef;
+import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.SystemApi;
 import android.annotation.TestApi;
@@ -91,7 +92,7 @@
      * Set all contents of this object to the contents of a NetworkCapabilities.
      * @hide
      */
-    public void set(NetworkCapabilities nc) {
+    public void set(@NonNull NetworkCapabilities nc) {
         mNetworkCapabilities = nc.mNetworkCapabilities;
         mTransportTypes = nc.mTransportTypes;
         mLinkUpBandwidthKbps = nc.mLinkUpBandwidthKbps;
@@ -405,7 +406,7 @@
      * @hide
      */
     @UnsupportedAppUsage
-    public NetworkCapabilities addCapability(@NetCapability int capability) {
+    public @NonNull NetworkCapabilities addCapability(@NetCapability int capability) {
         checkValidCapability(capability);
         mNetworkCapabilities |= 1 << capability;
         mUnwantedNetworkCapabilities &= ~(1 << capability);  // remove from unwanted capability list
@@ -442,7 +443,7 @@
      * @hide
      */
     @UnsupportedAppUsage
-    public NetworkCapabilities removeCapability(@NetCapability int capability) {
+    public @NonNull NetworkCapabilities removeCapability(@NetCapability int capability) {
         checkValidCapability(capability);
         final long mask = ~(1 << capability);
         mNetworkCapabilities &= mask;
@@ -456,7 +457,8 @@
      *
      * @hide
      */
-    public NetworkCapabilities setCapability(@NetCapability int capability, boolean value) {
+    public @NonNull NetworkCapabilities setCapability(@NetCapability int capability,
+            boolean value) {
         if (value) {
             addCapability(capability);
         } else {
@@ -534,7 +536,7 @@
     }
 
     /** Note this method may result in having the same capability in wanted and unwanted lists. */
-    private void combineNetCapabilities(NetworkCapabilities nc) {
+    private void combineNetCapabilities(@NonNull NetworkCapabilities nc) {
         this.mNetworkCapabilities |= nc.mNetworkCapabilities;
         this.mUnwantedNetworkCapabilities |= nc.mUnwantedNetworkCapabilities;
     }
@@ -546,7 +548,7 @@
      *
      * @hide
      */
-    public String describeFirstNonRequestableCapability() {
+    public @Nullable String describeFirstNonRequestableCapability() {
         final long nonRequestable = (mNetworkCapabilities | mUnwantedNetworkCapabilities)
                 & NON_REQUESTABLE_CAPABILITIES;
 
@@ -558,7 +560,8 @@
         return null;
     }
 
-    private boolean satisfiedByNetCapabilities(NetworkCapabilities nc, boolean onlyImmutable) {
+    private boolean satisfiedByNetCapabilities(@NonNull NetworkCapabilities nc,
+            boolean onlyImmutable) {
         long requestedCapabilities = mNetworkCapabilities;
         long requestedUnwantedCapabilities = mUnwantedNetworkCapabilities;
         long providedCapabilities = nc.mNetworkCapabilities;
@@ -572,12 +575,12 @@
     }
 
     /** @hide */
-    public boolean equalsNetCapabilities(NetworkCapabilities nc) {
+    public boolean equalsNetCapabilities(@NonNull NetworkCapabilities nc) {
         return (nc.mNetworkCapabilities == this.mNetworkCapabilities)
                 && (nc.mUnwantedNetworkCapabilities == this.mUnwantedNetworkCapabilities);
     }
 
-    private boolean equalsNetCapabilitiesRequestable(NetworkCapabilities that) {
+    private boolean equalsNetCapabilitiesRequestable(@NonNull NetworkCapabilities that) {
         return ((this.mNetworkCapabilities & ~NON_REQUESTABLE_CAPABILITIES) ==
                 (that.mNetworkCapabilities & ~NON_REQUESTABLE_CAPABILITIES))
                 && ((this.mUnwantedNetworkCapabilities & ~NON_REQUESTABLE_CAPABILITIES) ==
@@ -713,7 +716,7 @@
      * @hide
      */
     @UnsupportedAppUsage
-    public NetworkCapabilities addTransportType(@Transport int transportType) {
+    public @NonNull NetworkCapabilities addTransportType(@Transport int transportType) {
         checkValidTransportType(transportType);
         mTransportTypes |= 1 << transportType;
         setNetworkSpecifier(mNetworkSpecifier); // used for exception checking
@@ -727,7 +730,7 @@
      * @return This NetworkCapabilities instance, to facilitate chaining.
      * @hide
      */
-    public NetworkCapabilities removeTransportType(@Transport int transportType) {
+    public @NonNull NetworkCapabilities removeTransportType(@Transport int transportType) {
         checkValidTransportType(transportType);
         mTransportTypes &= ~(1 << transportType);
         setNetworkSpecifier(mNetworkSpecifier); // used for exception checking
@@ -740,7 +743,8 @@
      *
      * @hide
      */
-    public NetworkCapabilities setTransportType(@Transport int transportType, boolean value) {
+    public @NonNull NetworkCapabilities setTransportType(@Transport int transportType,
+            boolean value) {
         if (value) {
             addTransportType(transportType);
         } else {
@@ -757,7 +761,7 @@
      */
     @TestApi
     @SystemApi
-    public @Transport int[] getTransportTypes() {
+    @NonNull public @Transport int[] getTransportTypes() {
         return BitUtils.unpackBits(mTransportTypes);
     }
 
@@ -847,7 +851,7 @@
      * @param upKbps the estimated first hop upstream (device to network) bandwidth.
      * @hide
      */
-    public NetworkCapabilities setLinkUpstreamBandwidthKbps(int upKbps) {
+    public @NonNull NetworkCapabilities setLinkUpstreamBandwidthKbps(int upKbps) {
         mLinkUpBandwidthKbps = upKbps;
         return this;
     }
@@ -877,7 +881,7 @@
      * @param downKbps the estimated first hop downstream (network to device) bandwidth.
      * @hide
      */
-    public NetworkCapabilities setLinkDownstreamBandwidthKbps(int downKbps) {
+    public @NonNull NetworkCapabilities setLinkDownstreamBandwidthKbps(int downKbps) {
         mLinkDownBandwidthKbps = downKbps;
         return this;
     }
@@ -936,7 +940,7 @@
      * @return This NetworkCapabilities instance, to facilitate chaining.
      * @hide
      */
-    public NetworkCapabilities setNetworkSpecifier(NetworkSpecifier networkSpecifier) {
+    public @NonNull NetworkCapabilities setNetworkSpecifier(NetworkSpecifier networkSpecifier) {
         if (networkSpecifier != null && Long.bitCount(mTransportTypes) != 1) {
             throw new IllegalStateException("Must have a single transport specified to use " +
                     "setNetworkSpecifier");
@@ -955,20 +959,20 @@
      * @return This NetworkCapabilities instance, to facilitate chaining.
      * @hide
      */
-    public NetworkCapabilities setTransportInfo(TransportInfo transportInfo) {
+    public @NonNull NetworkCapabilities setTransportInfo(TransportInfo transportInfo) {
         mTransportInfo = transportInfo;
         return this;
     }
 
     /**
-     * Gets the optional bearer specific network specifier.
+     * Gets the optional bearer specific network specifier. May be {@code null} if not set.
      *
      * @return The optional {@link NetworkSpecifier} specifying the bearer specific network
-     *         specifier. See {@link #setNetworkSpecifier}.
+     *         specifier or {@code null}. See {@link #setNetworkSpecifier}.
      * @hide
      */
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023)
-    public NetworkSpecifier getNetworkSpecifier() {
+    public @Nullable NetworkSpecifier getNetworkSpecifier() {
         return mNetworkSpecifier;
     }
 
@@ -1015,8 +1019,6 @@
     /**
      * Magic value that indicates no signal strength provided. A request specifying this value is
      * always satisfied.
-     *
-     * @hide
      */
     public static final int SIGNAL_STRENGTH_UNSPECIFIED = Integer.MIN_VALUE;
 
@@ -1024,7 +1026,7 @@
      * Signal strength. This is a signed integer, and higher values indicate better signal.
      * The exact units are bearer-dependent. For example, Wi-Fi uses RSSI.
      */
-    @UnsupportedAppUsage
+    @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P)
     private int mSignalStrength = SIGNAL_STRENGTH_UNSPECIFIED;
 
     /**
@@ -1041,7 +1043,7 @@
      * @hide
      */
     @UnsupportedAppUsage
-    public NetworkCapabilities setSignalStrength(int signalStrength) {
+    public @NonNull NetworkCapabilities setSignalStrength(int signalStrength) {
         mSignalStrength = signalStrength;
         return this;
     }
@@ -1060,9 +1062,7 @@
      * Retrieves the signal strength.
      *
      * @return The bearer-specific signal strength.
-     * @hide
      */
-    @SystemApi
     public int getSignalStrength() {
         return mSignalStrength;
     }
@@ -1120,7 +1120,7 @@
      * Convenience method to set the UIDs this network applies to to a single UID.
      * @hide
      */
-    public NetworkCapabilities setSingleUid(int uid) {
+    public @NonNull NetworkCapabilities setSingleUid(int uid) {
         final ArraySet<UidRange> identity = new ArraySet<>(1);
         identity.add(new UidRange(uid, uid));
         setUids(identity);
@@ -1132,7 +1132,7 @@
      * This makes a copy of the set so that callers can't modify it after the call.
      * @hide
      */
-    public NetworkCapabilities setUids(Set<UidRange> uids) {
+    public @NonNull NetworkCapabilities setUids(Set<UidRange> uids) {
         if (null == uids) {
             mUids = null;
         } else {
@@ -1146,7 +1146,7 @@
      * This returns a copy of the set so that callers can't modify the original object.
      * @hide
      */
-    public Set<UidRange> getUids() {
+    public @Nullable Set<UidRange> getUids() {
         return null == mUids ? null : new ArraySet<>(mUids);
     }
 
@@ -1179,7 +1179,7 @@
      * @hide
      */
     @VisibleForTesting
-    public boolean equalsUids(NetworkCapabilities nc) {
+    public boolean equalsUids(@NonNull NetworkCapabilities nc) {
         Set<UidRange> comparedUids = nc.mUids;
         if (null == comparedUids) return null == mUids;
         if (null == mUids) return false;
@@ -1212,7 +1212,7 @@
      * @see #appliesToUid
      * @hide
      */
-    public boolean satisfiedByUids(NetworkCapabilities nc) {
+    public boolean satisfiedByUids(@NonNull NetworkCapabilities nc) {
         if (null == nc.mUids || null == mUids) return true; // The network satisfies everything.
         for (UidRange requiredRange : mUids) {
             if (requiredRange.contains(nc.mEstablishingVpnAppUid)) return true;
@@ -1232,7 +1232,7 @@
      * @hide
      */
     @VisibleForTesting
-    public boolean appliesToUidRange(UidRange requiredRange) {
+    public boolean appliesToUidRange(@Nullable UidRange requiredRange) {
         if (null == mUids) return true;
         for (UidRange uidRange : mUids) {
             if (uidRange.containsRange(requiredRange)) {
@@ -1247,7 +1247,7 @@
      * NetworkCapabilities apply to.
      * nc is assumed nonnull.
      */
-    private void combineUids(NetworkCapabilities nc) {
+    private void combineUids(@NonNull NetworkCapabilities nc) {
         if (null == nc.mUids || null == mUids) {
             mUids = null;
             return;
@@ -1268,7 +1268,7 @@
      * Sets the SSID of this network.
      * @hide
      */
-    public NetworkCapabilities setSSID(String ssid) {
+    public @NonNull NetworkCapabilities setSSID(@Nullable String ssid) {
         mSSID = ssid;
         return this;
     }
@@ -1277,7 +1277,7 @@
      * Gets the SSID of this network, or null if none or unknown.
      * @hide
      */
-    public String getSSID() {
+    public @Nullable String getSSID() {
         return mSSID;
     }
 
@@ -1285,7 +1285,7 @@
      * Tests if the SSID of this network is the same as the SSID of the passed network.
      * @hide
      */
-    public boolean equalsSSID(NetworkCapabilities nc) {
+    public boolean equalsSSID(@NonNull NetworkCapabilities nc) {
         return Objects.equals(mSSID, nc.mSSID);
     }
 
@@ -1293,7 +1293,7 @@
      * Check if the SSID requirements of this object are matched by the passed object.
      * @hide
      */
-    public boolean satisfiedBySSID(NetworkCapabilities nc) {
+    public boolean satisfiedBySSID(@NonNull NetworkCapabilities nc) {
         return mSSID == null || mSSID.equals(nc.mSSID);
     }
 
@@ -1304,7 +1304,7 @@
      * equal.
      * @hide
      */
-    private void combineSSIDs(NetworkCapabilities nc) {
+    private void combineSSIDs(@NonNull NetworkCapabilities nc) {
         if (mSSID != null && !mSSID.equals(nc.mSSID)) {
             throw new IllegalStateException("Can't combine two SSIDs");
         }
@@ -1319,7 +1319,7 @@
      * both lists will never be satisfied.
      * @hide
      */
-    public void combineCapabilities(NetworkCapabilities nc) {
+    public void combineCapabilities(@NonNull NetworkCapabilities nc) {
         combineNetCapabilities(nc);
         combineTransportTypes(nc);
         combineLinkBandwidths(nc);
@@ -1359,7 +1359,7 @@
      */
     @TestApi
     @SystemApi
-    public boolean satisfiedByNetworkCapabilities(NetworkCapabilities nc) {
+    public boolean satisfiedByNetworkCapabilities(@Nullable NetworkCapabilities nc) {
         return satisfiedByNetworkCapabilities(nc, false);
     }
 
@@ -1370,7 +1370,7 @@
      *
      * @hide
      */
-    public boolean satisfiedByImmutableNetworkCapabilities(NetworkCapabilities nc) {
+    public boolean satisfiedByImmutableNetworkCapabilities(@Nullable NetworkCapabilities nc) {
         return satisfiedByNetworkCapabilities(nc, true);
     }
 
@@ -1381,7 +1381,7 @@
      *
      * @hide
      */
-    public String describeImmutableDifferences(NetworkCapabilities that) {
+    public String describeImmutableDifferences(@Nullable NetworkCapabilities that) {
         if (that == null) {
             return "other NetworkCapabilities was null";
         }
@@ -1420,7 +1420,7 @@
      *
      * @hide
      */
-    public boolean equalRequestableCapabilities(NetworkCapabilities nc) {
+    public boolean equalRequestableCapabilities(@Nullable NetworkCapabilities nc) {
         if (nc == null) return false;
         return (equalsNetCapabilitiesRequestable(nc) &&
                 equalsTransportTypes(nc) &&
@@ -1428,7 +1428,7 @@
     }
 
     @Override
-    public boolean equals(Object obj) {
+    public boolean equals(@Nullable Object obj) {
         if (obj == null || (obj instanceof NetworkCapabilities == false)) return false;
         NetworkCapabilities that = (NetworkCapabilities) obj;
         return (equalsNetCapabilities(that)
@@ -1502,7 +1502,7 @@
         };
 
     @Override
-    public String toString() {
+    public @NonNull String toString() {
         final StringBuilder sb = new StringBuilder("[");
         if (0 != mTransportTypes) {
             sb.append(" Transports: ");
@@ -1561,8 +1561,8 @@
     /**
      * @hide
      */
-    public static void appendStringRepresentationOfBitMaskToStringBuilder(StringBuilder sb,
-            long bitMask, NameOf nameFetcher, String separator) {
+    public static void appendStringRepresentationOfBitMaskToStringBuilder(@NonNull StringBuilder sb,
+            long bitMask, @NonNull NameOf nameFetcher, @NonNull String separator) {
         int bitPos = 0;
         boolean firstElementAdded = false;
         while (bitMask != 0) {
@@ -1580,7 +1580,7 @@
     }
 
     /** @hide */
-    public void writeToProto(ProtoOutputStream proto, long fieldId) {
+    public void writeToProto(@NonNull ProtoOutputStream proto, long fieldId) {
         final long token = proto.start(fieldId);
 
         for (int transport : getTransportTypes()) {
@@ -1610,7 +1610,7 @@
     /**
      * @hide
      */
-    public static String capabilityNamesOf(@NetCapability int[] capabilities) {
+    public static @NonNull String capabilityNamesOf(@Nullable @NetCapability int[] capabilities) {
         StringJoiner joiner = new StringJoiner("|");
         if (capabilities != null) {
             for (int c : capabilities) {
@@ -1623,7 +1623,7 @@
     /**
      * @hide
      */
-    public static String capabilityNameOf(@NetCapability int capability) {
+    public static @NonNull String capabilityNameOf(@NetCapability int capability) {
         switch (capability) {
             case NET_CAPABILITY_MMS:                  return "MMS";
             case NET_CAPABILITY_SUPL:                 return "SUPL";
@@ -1658,7 +1658,7 @@
      * @hide
      */
     @UnsupportedAppUsage
-    public static String transportNamesOf(@Transport int[] types) {
+    public static @NonNull String transportNamesOf(@Nullable @Transport int[] types) {
         StringJoiner joiner = new StringJoiner("|");
         if (types != null) {
             for (int t : types) {
@@ -1671,7 +1671,7 @@
     /**
      * @hide
      */
-    public static String transportNameOf(@Transport int transport) {
+    public static @NonNull String transportNameOf(@Transport int transport) {
         if (!isValidTransport(transport)) {
             return "UNKNOWN";
         }