code: protected String errorMessage(String input, Exception e) {
          return String.format("Invalid parameter: %s (%s)", input, e.getMessage());
      }
docs: Given a string representation which was unable to be parsed and the exception thrown, produce
  an entity to be sent to the client.
  
  @param input the raw input value
  @param e the exception thrown while parsing {@code input}
  @return the error message to be sent the client