code: @Nullable
    public <T> T execute (@Nonnull final HttpUriRequest aRequest,
                          @Nonnull final ResponseHandler <T> aResponseHandler) throws IOException
    {
      return execute (aRequest, (HttpContext) null, aResponseHandler);
    }
docs: Execute the provided request without any special context. The response
  handler is invoked as a callback. This method automatically cleans up all
  used resources and as such is preferred over the execute methods returning
  the CloseableHttpResponse.
  
  @param aRequest
  The request to be executed. May not be <code>null</code>.
  @param aResponseHandler
  The response handler to be executed. May not be <code>null</code>.
  @return The evaluated response of the response handler. May be
  <code>null</code>.
  @throws IOException
  In case of error
  @throws IllegalStateException
  If this manager was already closed!
  @param <T>
  return type