code: public static Map.Entry<String, Object> value(String key, Object value) {
          return new AbstractMap.SimpleImmutableEntry<>(key, value);
      }
docs: This is a auxiliary method used to load the {@code Map} returned from {@code payloadFactory}. The usage
  is similar to {@code Map} interaction, but its simplify the dynamic usage of {@code payloadFactory}.
  
  @param   key
  {@code String} the attribute key.
  
  @param   value
  {@code Object} the attribute value.
  
  @return  {@code Map.Entry<String, Object>}