Blank string is set as null

I was wondering what the reasoning behind these lines were: http://pastie.org/6077984

I consider there to be a pretty big difference between null and ''. I realize that for the majority of php functions php will cast null to '' and so everyone is happy, but certain functions like is_null are not so kind. On top of that, any user function that expects a difference between null and '' will be a source of bugs.

So this to me doesn't make sense in the code. I frequently miss things though so is there something I have missed?

<3 Austin