code: public static InvocationResponse error(String errorMessage) {
  		InvocationResponse resp = new InvocationResponse(ERROR);
  		resp.errorMessage = errorMessage;
  		return resp;
  	}
docs: Creates a new {@link InvocationResponse} to hold the error that occurred
  during the execution of the service.
  
  @param errorMessage
  - the error message that describes the occurred error.
  @return the invocation request.