Remove NullObjectReceiveStatistics() in rtp_rtcp module

webrtc/modules/rtp_rtcp/include/rtp_rtcp.h

 /*
  *  Copyright (c) 2012 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 37 matching lines @@
     Configuration();
 
     // True for a audio version of the RTP/RTCP module object false will create
     // a video version.
     bool audio = false;
     bool receiver_only = false;
 
     // The clock to use to read time. If nullptr then system clock will be used.
     Clock* clock = nullptr;
 
-    ReceiveStatistics* receive_statistics;
+    ReceiveStatistics* receive_statistics = nullptr;
 
     // Transport object that will be called when packets are ready to be sent
     // out on the network.
     Transport* outgoing_transport = nullptr;
 
     // Called when the receiver request a intra frame.
     RtcpIntraFrameObserver* intra_frame_callback = nullptr;
 
     // Called when we receive a changed estimate from the receiver of out
     // stream.
@@ skipping 394 matching lines @@
   virtual int32_t SetKeyFrameRequestMethod(KeyFrameRequestMethod method) = 0;
 
   // Sends a request for a keyframe.
   // Returns -1 on failure else 0.
   virtual int32_t RequestKeyFrame() = 0;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RTCP_H_