question: public < T > List < String > validateBean ( T bean , String errIfBeanNull ) { List < String > errors = new ArrayList < String > ( ) ; if ( bean == null ) { errors . add ( errIfBeanNull ) ; return errors ; } Set < ConstraintViolation < T > > violations = validator . validate ( bean ) ; for ( ConstraintViolation < T > violation : violations ) { errors . add ( violation . getMessage ( ) ) ; } return errors ; }
target:  validate the bean is not null; then validate its fields