Adding nullObject and undefinedObjects functions as predicated to check ...

...if var is null or undefined.

nullObject & undefinedObjects function were taken from [underscore](https://github.com/jashkenas/underscore/blob/master/underscore.js#L1108)  so they are well tested, i did not use null or undefined in the predicates object as [property names to avoid confusion](http://stackoverflow.com/questions/7022397/using-reserved-words-as-property-names-revisited).