unexpected behavior isNull and notNull

[mren]

isNull and notNull are implemented in this way

notNull: function(str) {
    return str !== '';
},
isNull: function(str) {
    return str === '';
},

which checks if the string is empty and not if the object is null.
Wouldn't be

isNull: function(str) {
    return str === null;
},
notNull: function(str) {
    return !validators.isNull(str);
}

be more consistent with the validation name?

[chriso]

Validator input is coerced before ever getting to that stage so that all of the weird potential inputs are handled correctly - undefined, null, NaN, etc.