Allow passing null for RTCcodecSpecific info in encoder callback.

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCVideoCodec.h

 /*
  *  Copyright 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 66 matching lines @@
 
 RTC_EXPORT
 @interface RTCCodecSpecificInfoH264 : NSObject<RTCCodecSpecificInfo>
 
 @property(nonatomic, assign) RTCH264PacketizationMode packetizationMode;
 
 @end
 
 /** Callback block for encoder. */
 typedef BOOL (^RTCVideoEncoderCallback)(RTCEncodedImage *frame,
-                                        id<RTCCodecSpecificInfo> info,
+                                        _Nullable id<RTCCodecSpecificInfo> info,
                                         RTCRtpFragmentationHeader *header);
 
 /** Callback block for decoder. */
 typedef void (^RTCVideoDecoderCallback)(RTCVideoFrame *frame);
 
 typedef NS_ENUM(NSUInteger, RTCVideoCodecMode) {
   RTCVideoCodecModeRealtimeVideo,
   RTCVideoCodecModeScreensharing,
 };
 
@@ skipping 77 matching lines @@
 - (NSInteger)decode:(RTCEncodedImage *)encodedImage
           missingFrames:(BOOL)missingFrames
     fragmentationHeader:(RTCRtpFragmentationHeader *)fragmentationHeader
       codecSpecificInfo:(__nullable id<RTCCodecSpecificInfo>)info
            renderTimeMs:(int64_t)renderTimeMs;
 - (NSString *)implementationName;
 
 @end
 
 NS_ASSUME_NONNULL_END