Fixing some of the issues found by clang static analyzer.

Bug: webrtc:8737
Change-Id: Ib436449c493336e7c35a72a96dc88cccdbb5bbaf
Reviewed-on: https://webrtc-review.googlesource.com/39200
Commit-Queue: Peter Hanspers <peterhanspers@webrtc.org>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21607}
diff --git a/sdk/objc/Framework/Classes/PeerConnection/RTCWrappedNativeVideoEncoder.mm b/sdk/objc/Framework/Classes/PeerConnection/RTCWrappedNativeVideoEncoder.mm
index 9d2f81b..8988e6d 100644
--- a/sdk/objc/Framework/Classes/PeerConnection/RTCWrappedNativeVideoEncoder.mm
+++ b/sdk/objc/Framework/Classes/PeerConnection/RTCWrappedNativeVideoEncoder.mm
@@ -47,7 +47,7 @@
 }
 
 - (NSInteger)encode:(RTCVideoFrame *)frame
-    codecSpecificInfo:(id<RTCCodecSpecificInfo>)info
+    codecSpecificInfo:(nullable id<RTCCodecSpecificInfo>)info
            frameTypes:(NSArray<NSNumber *> *)frameTypes {
   RTC_NOTREACHED();
   return 0;