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

webrtc/common_audio/signal_processing/include/real_fft.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 39 matching lines @@
 //   real_data_in - the input signal. For an ARM Neon platform, it must be
 //                  aligned on a 32-byte boundary.
 //
 // Output Arguments:
 //   complex_data_out - the output complex signal with (2^order + 2) 16-bit
 //                      elements. For an ARM Neon platform, it must be different
 //                      from real_data_in, and aligned on a 32-byte boundary.
 //
 // Return Value:
 //   0  - FFT calculation is successful.
-//   -1 - Error with bad arguments (NULL pointers).
+//   -1 - Error with bad arguments (null pointers).
 int WebRtcSpl_RealForwardFFT(struct RealFFT* self,
                              const int16_t* real_data_in,
                              int16_t* complex_data_out);
 
 // Compute the inverse FFT for a conjugate-symmetric input sequence of length of
 // 2^order, where 1 < order <= MAX_FFT_ORDER. Transform length is determined by
 // the specification structure, which must be initialized prior to calling the
 // FFT function with WebRtcSpl_CreateRealFFT().
 // For a transform of length M, the input sequence is represented using a packed
 // CCS vector of length M+2, which is explained in the comments for
 // WebRtcSpl_RealForwardFFTC above.
 //
 // Input Arguments:
 //   self - pointer to preallocated and initialized FFT specification structure.
 //   complex_data_in - the input complex signal with (2^order + 2) 16-bit
 //                     elements. For an ARM Neon platform, it must be aligned on
 //                     a 32-byte boundary.
 //
 // Output Arguments:
 //   real_data_out - the output real signal. For an ARM Neon platform, it must
 //                   be different to complex_data_in, and aligned on a 32-byte
 //                   boundary.
 //
 // Return Value:
 //   0 or a positive number - a value that the elements in the |real_data_out|
 //                            should be shifted left with in order to get
 //                            correct physical values.
-//   -1 - Error with bad arguments (NULL pointers).
+//   -1 - Error with bad arguments (null pointers).
 int WebRtcSpl_RealInverseFFT(struct RealFFT* self,
                              const int16_t* complex_data_in,
                              int16_t* real_data_out);
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif  // WEBRTC_COMMON_AUDIO_SIGNAL_PROCESSING_INCLUDE_REAL_FFT_H_