code: public static <MESSAGE, KEY> KeyReader<MESSAGE, KEY> forMessage(
              final Class<MESSAGE> messageClass,
              final KeyExtractFunction<MESSAGE, KEY> extractFunction) {
          return FunctionKeyReader.create(messageClass, extractFunction);
      }
docs: Create a new key reader for a specific message class.
  @param messageClass The class of the message for which a key reader is to be created.
  @param extractFunction The function to use to extract a saga instance key from a message.
  @param <MESSAGE> The type of the message this reader is for.
  @param <KEY> The type of the key to be extracted.
  @return Returns a new key reader instance.