Replace NULL with nullptr in all C++ files.

webrtc/modules/rtp_rtcp/source/ulpfec_generator_unittest.cc

Index: webrtc/modules/rtp_rtcp/source/ulpfec_generator_unittest.cc
diff --git a/webrtc/modules/rtp_rtcp/source/ulpfec_generator_unittest.cc b/webrtc/modules/rtp_rtcp/source/ulpfec_generator_unittest.cc
index 3712a373a52a63b9f05cec710b3e4b35b1c2b5e5..e4d403c3e173173078d3c29b13da8ccf4e70064f 100644
--- a/webrtc/modules/rtp_rtcp/source/ulpfec_generator_unittest.cc
+++ b/webrtc/modules/rtp_rtcp/source/ulpfec_generator_unittest.cc
@@ -38,7 +38,7 @@ void VerifyHeader(uint16_t seq_num,
                   RedPacket* packet,
                   bool marker_bit) {
   EXPECT_GT(packet->length(), kRtpHeaderSize);
-  EXPECT_TRUE(packet->data() != NULL);
+  EXPECT_TRUE(packet->data() != nullptr);
   uint8_t* data = packet->data();
   // Marker bit not set.
   EXPECT_EQ(marker_bit ? 0x80 : 0, data[1] & 0x80);