Fixing double standard with nil handling.

Noticed a double standard when it cam to nil handling on the two initialiser methods.

`.new` just checks for the presence of the field, where as `.with` checks for a truthy value for the field.

Not to sure if you want to go this way or make `.new` check the value as well. I just though it was a little weird I could get away with one and not the other.

-- Chris