code: private URI getHasMemberFromRequest(final HttpServletRequest request) throws IOException {
          final String baseUri = request.getRequestURL().toString();
          final RDFReader reader;
          final String contentType = request.getContentType();
          final Lang format = contentTypeToLang(contentType);
          final Model inputModel;
          try {
              inputModel = createDefaultModel();
              reader = inputModel.getReader(format.getName().toUpperCase());
              reader.read(inputModel, request.getInputStream(), baseUri);
              final Statement st = inputModel.getProperty(null, MEMBERSHIP_RESOURCE);
              return (st != null ? URI.create(st.getObject().toString()) : null);
          } catch (final RiotException e) {
              throw new BadRequestException("RDF was not parsable: " + e.getMessage(), e);
          } catch (final RuntimeIOException e) {
              if (e.getCause() instanceof JsonParseException) {
                  throw new MalformedRdfException(e.getCause());
              }
              throw new RepositoryRuntimeException(e);
          }
      }
docs: Get the memberRelation object from the contents.
  
  @param baseUri The current request URL
  @param body The request body
  @param contentType The content type.
  @return The URI of the memberRelation object
  @throws IOException when getting request's inputstream