Validators return true on isValid if value is null

timvw · **Posted:** Sat Jan 28, 2006 10:41 am

When i apply an annotation validator on a property, the validator will return true if the property is null.

Eg:

Code:

@ManyToMany
@Size(min=1) public List getUsers() { return users; }

When users = null, the validator will return true. I would expect it returns false because we don't know for sure that the size is at least 1.

I know that the documentation says that the @Size annotation should only be used on type array, list or map. One could argue that null is not an applicable type. But even then i would expect isValidate to return false because the value isn't applicable.

It appears this was already the intention of the author, because when i look at PatternValidator i see the following: (The value isn't applicable, thus isValid return false)

Code:

if ( !( value instanceof String ) ) return false;

Thus i wonder: Why do all the Validators return true when the value is null?

emmanuel · **Posted:** Mon Jan 30, 2006 10:06 am

negative, add @NotNull for this behavior

timvw · **Posted:** Mon Jan 30, 2006 4:48 pm

Thanks, i had already done that :) It just didn't feel very right the way the other validators behave on null.. But i'll get used to it.

timvw · **Posted:** Mon Jan 30, 2006 6:15 pm

What i still ask myself: is there a particular reason to give null a special treatment than other values that are not applicable?

Eg: LengthValidator will return true for null and false for other values that aren't instanceof String either...

Code:

public boolean isValid(Object value) {
  if ( value == null ) return true;
  if ( !( value instanceof String ) ) return false;
  String string = (String) value;
  int length = string.length();
  return length >= min && length <= max;
}

emmanuel · **Posted:** Tue Jan 31, 2006 6:08 am

Yes. Null semantically means I don't know the information.
If you don't know the value why raising an invalid exception.

timvw · **Posted:** Tue Jan 31, 2006 7:27 am

emmanuel wrote:

Yes. Null semantically means I don't know the information.
If you don't know the value why raising an invalid exception.

For me it would be the ultimate reason to throw that exception. If i don't know the value, how can i be sure it isn't violating the constraint?

I can understand your POV: because you're not sure that it is valid or not, you decide to let it in anyway (blacklist). I prefer the approach to keep it out untill i'm absolutely sure that it's valid (whitelist).

emmanuel · **Posted:** Wed Feb 01, 2006 4:51 am

This is not how ternary logic works