Replace NULL with nullptr in all C++ files.

webrtc/modules/audio_coding/neteq/audio_multi_vector_unittest.cc

Index: webrtc/modules/audio_coding/neteq/audio_multi_vector_unittest.cc
diff --git a/webrtc/modules/audio_coding/neteq/audio_multi_vector_unittest.cc b/webrtc/modules/audio_coding/neteq/audio_multi_vector_unittest.cc
index af8d5f1b9828818b67a89296196ac43f51195192..91f338e7025b5c50991d59af575bbe1bba89b10c 100644
--- a/webrtc/modules/audio_coding/neteq/audio_multi_vector_unittest.cc
+++ b/webrtc/modules/audio_coding/neteq/audio_multi_vector_unittest.cc
@@ -122,10 +122,10 @@ TEST_P(AudioMultiVectorTest, PushBackInterleavedAndCopy) {
   EXPECT_TRUE(vec_copy.Empty());
 }
 
-// Try to copy to a NULL pointer. Nothing should happen.
+// Try to copy to a null pointer. Nothing should happen.
 TEST_P(AudioMultiVectorTest, CopyToNull) {
   AudioMultiVector vec(num_channels_);
-  AudioMultiVector* vec_copy = NULL;
+  AudioMultiVector* vec_copy = nullptr;
   vec.PushBackInterleaved(array_interleaved_, interleaved_length_);
   vec.CopyTo(vec_copy);
 }