code: @Override
      public HttpContent readChunk(ByteBufAllocator allocator) throws Exception {
          if (isLastChunkSent) {
              return null;
          } else {
              HttpContent nextChunk = nextChunk();
              globalProgress += nextChunk.content().readableBytes();
              return nextChunk;
          }
      }
docs: Returns the next available HttpChunk. The caller is responsible to test if this chunk is the last one (isLast()),
  in order to stop calling this getMethod.
  
  @return the next available HttpChunk
  @throws ErrorDataEncoderException
  if the encoding is in error