Fix incorrect nullity check.
Fix incorrect nullity check.

https://code.google.com/p/morelinq/source/detail?r=c9dac594b968ca33622b37c28ee28b2e5c50abb2

anders9ustafsson/morelinq-portable,anders9ustafsson/morelinq-portable,anders9ustafsson/morelinq-portable