public static NestableFieldValidator fv(final Class cls, final boolean nullAllowed) {
        return new NestableFieldValidator() {
            @Override
            public void validateField(String pd, String name, Object field) throws IllegalArgumentException {
                if (nullAllowed && field == null) {
                    return;
                }
                if (!cls.isInstance(field)) {
                    throw new IllegalArgumentException(pd + name + " must be a " + cls.getName() + ". (" + field + ")");
                }
            }
        };
    }
public static NestableFieldValidator fv ( final Class cls , final boolean nullAllowed ) { return new NestableFieldValidator ( ) { @ Override public void validateField ( String pd , String name , Object field ) throws IllegalArgumentException { if ( nullAllowed && field == null ) { return ; } if ( ! cls . isInstance ( field ) ) { throw new IllegalArgumentException ( pd + name + " must be a " + cls . getName ( ) + ". (" + field + ")" ) ; } } } ; }
Returns a new NestableFieldValidator for a given class.

@param cls         the Class the field should be a type of
@param nullAllowed whether or not a value of null is valid
@return a NestableFieldValidator for that class