Fix compile

src/core/ext/transport/chttp2/transport/chttp2_transport.c

@@ -1230,8 +1230,9 @@ static void perform_stream_op_locked(grpc_exec_ctx *exec_ctx, void *stream_op,
           GPR_ASSERT(s->id != 0);
           grpc_chttp2_stream_write_type write_type =
               GRPC_CHTTP2_STREAM_WRITE_INITIATE_COVERED;
-          if (op->send_message != NULL &&
-              (op->send_message->flags & GRPC_WRITE_BUFFER_HINT)) {
+          if (op->send_message &&
+              (op->payload->send_message.send_message->flags &
+               GRPC_WRITE_BUFFER_HINT)) {
             write_type = GRPC_CHTTP2_STREAM_WRITE_PIGGYBACK;
           }
           grpc_chttp2_become_writable(exec_ctx, t, s, write_type,