Codechange: Use null pointer literal instead of the NULL macro

src/network/core/tcp_admin.cpp

@@ -115,7 +115,7 @@ NetworkRecvStatus NetworkAdminSocketHandler::HandlePacket(Packet *p)
 NetworkRecvStatus NetworkAdminSocketHandler::ReceivePackets()
 {
 	Packet *p;
-	while ((p = this->ReceivePacket()) != NULL) {
+	while ((p = this->ReceivePacket()) != nullptr) {
 		NetworkRecvStatus res = this->HandlePacket(p);
 		if (res != NETWORK_RECV_STATUS_OKAY) return res;
 	}