code: public boolean remove() {
          Entry e = flushedEntry;
          if (e == null) {
              clearNioBuffers();
              return false;
          }
          Object msg = e.msg;
  
          ChannelPromise promise = e.promise;
          int size = e.pendingSize;
  
          removeEntry(e);
  
          if (!e.cancelled) {
              // only release message, notify and decrement if it was not canceled before.
              ReferenceCountUtil.safeRelease(msg);
              safeSuccess(promise);
              decrementPendingOutboundBytes(size, false, true);
          }
  
          // recycle the entry
          e.recycle();
  
          return true;
      }
docs: Will remove the current message, mark its {@link ChannelPromise} as success and return {@code true}. If no
  flushed message exists at the time this method is called it will return {@code false} to signal that no more
  messages are ready to be handled.