@ExceptionHandler(ValidationException.class)
    public ResponseEntity<ErrorResponse> toResponse(
            HttpServletRequest request, ValidationException exception) {
        logException(request, exception);

        HttpStatus httpStatus;

        if (exception instanceof ConstraintViolationException) {
            httpStatus = HttpStatus.BAD_REQUEST;
        } else {
            httpStatus = HttpStatus.INTERNAL_SERVER_ERROR;
            Monitors.error("error", "error");
        }

        return new ResponseEntity<>(toErrorResponse(exception), httpStatus);
    }
This class converts Hibernate {@link ValidationException} into http response.
rest/src/main/java/com/netflix/conductor/rest/controllers/ValidationExceptionMapper.java