Replace NULL with nullptr or null in webrtc/audio/ and common_audio/.

webrtc/common_audio/vad/include/webrtc_vad.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 21 matching lines @@
 // Frees the dynamic memory of a specified VAD instance.
 //
 // - handle [i] : Pointer to VAD instance that should be freed.
 void WebRtcVad_Free(VadInst* handle);
 
 // Initializes a VAD instance.
 //
 // - handle [i/o] : Instance that should be initialized.
 //
 // returns        : 0 - (OK),
-//                 -1 - (NULL pointer or Default mode could not be set).
+//                 -1 - (null pointer or Default mode could not be set).
 int WebRtcVad_Init(VadInst* handle);
 
 // Sets the VAD operating mode. A more aggressive (higher mode) VAD is more
 // restrictive in reporting speech. Put in other words the probability of being
 // speech when the VAD returns 1 is increased with increasing mode. As a
 // consequence also the missed detection rate goes up.
 //
 // - handle [i/o] : VAD instance.
 // - mode   [i]   : Aggressiveness mode (0, 1, 2, or 3).
 //
 // returns        : 0 - (OK),
-//                 -1 - (NULL pointer, mode could not be set or the VAD instance
+//                 -1 - (null pointer, mode could not be set or the VAD instance
 //                       has not been initialized).
 int WebRtcVad_set_mode(VadInst* handle, int mode);
 
 // Calculates a VAD decision for the |audio_frame|. For valid sampling rates
 // frame lengths, see the description of WebRtcVad_ValidRatesAndFrameLengths().
 //
 // - handle       [i/o] : VAD Instance. Needs to be initialized by
 //                        WebRtcVad_Init() before call.
 // - fs           [i]   : Sampling frequency (Hz): 8000, 16000, or 32000
 // - audio_frame  [i]   : Audio frame buffer.
@@ skipping 12 matching lines @@
 // - frame_length [i] : Speech frame buffer length in number of samples.
 //
 // returns            : 0 - (valid combination), -1 - (invalid combination)
 int WebRtcVad_ValidRateAndFrameLength(int rate, size_t frame_length);
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif  // WEBRTC_COMMON_AUDIO_VAD_INCLUDE_WEBRTC_VAD_H_  // NOLINT