code: private MediaType acceptabePlainTextMediaType() {
          final List<MediaType> acceptable = headers.getAcceptableMediaTypes();
          if (acceptable == null || acceptable.size() == 0) {
              return TEXT_PLAIN_TYPE;
          }
          for (final MediaType type : acceptable) {
              if (type.isWildcardType() || (type.isCompatible(TEXT_PLAIN_TYPE) && type.isWildcardSubtype())) {
                  return TEXT_PLAIN_TYPE;
              } else if (type.isCompatible(TEXT_PLAIN_TYPE)) {
                  return type;
              }
          }
          return null;
      }
docs: Returns an acceptable plain text media type if possible, or null if not.
  @return an acceptable plain-text media type, or null