Replace NULL with nullptr in all C++ files.

webrtc/modules/rtp_rtcp/source/rtp_format.cc

 /*
  *  Copyright (c) 2014 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 20 matching lines @@
       RTC_CHECK(rtp_type_header);
       return new RtpPacketizerVp8(rtp_type_header->VP8, max_payload_len);
     case kRtpVideoVp9:
       RTC_CHECK(rtp_type_header);
       return new RtpPacketizerVp9(rtp_type_header->VP9, max_payload_len);
     case kRtpVideoGeneric:
       return new RtpPacketizerGeneric(frame_type, max_payload_len);
     case kRtpVideoNone:
       RTC_NOTREACHED();
   }
-  return NULL;
+  return nullptr;
 }
 
 RtpDepacketizer* RtpDepacketizer::Create(RtpVideoCodecTypes type) {
   switch (type) {
     case kRtpVideoH264:
       return new RtpDepacketizerH264();
     case kRtpVideoVp8:
       return new RtpDepacketizerVp8();
     case kRtpVideoVp9:
       return new RtpDepacketizerVp9();
     case kRtpVideoGeneric:
       return new RtpDepacketizerGeneric();
     case kRtpVideoNone:
       assert(false);
   }
-  return NULL;
+  return nullptr;
 }
 }  // namespace webrtc