Annotate libjingle_peerconnection_java with @Nullable.

Bug: webrtc:8881
Change-Id: Ida2ef6c003567d19529c21629c916ed40e8de3a6
Reviewed-on: https://webrtc-review.googlesource.com/63380
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Paulina Hensman <phensman@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22563}
diff --git a/sdk/android/api/org/webrtc/RtpReceiver.java b/sdk/android/api/org/webrtc/RtpReceiver.java
index f33fa58..b770519 100644
--- a/sdk/android/api/org/webrtc/RtpReceiver.java
+++ b/sdk/android/api/org/webrtc/RtpReceiver.java
@@ -10,6 +10,7 @@
 
 package org.webrtc;
 
+import javax.annotation.Nullable;
 import org.webrtc.MediaStreamTrack;
 
 /** Java wrapper for a C++ RtpReceiverInterface. */
@@ -25,7 +26,7 @@
   final long nativeRtpReceiver;
   private long nativeObserver;
 
-  private MediaStreamTrack cachedTrack;
+  @Nullable private MediaStreamTrack cachedTrack;
 
   @CalledByNative
   public RtpReceiver(long nativeRtpReceiver) {
@@ -34,11 +35,12 @@
     cachedTrack = MediaStreamTrack.createMediaStreamTrack(nativeTrack);
   }
 
+  @Nullable
   public MediaStreamTrack track() {
     return cachedTrack;
   }
 
-  public boolean setParameters(RtpParameters parameters) {
+  public boolean setParameters(@Nullable RtpParameters parameters) {
     return parameters == null ? false : nativeSetParameters(nativeRtpReceiver, parameters);
   }