writeField:(id)field raises exception if first line of CSV has any null field

[Motti-Shneor]

the relatively new if (_currentLine == 0) { [_firstLineKeys addObject:field]; }

doesn't check for nils - and NSArray raises on field==nil.

[Motti-Shneor]

I really need a fix for this one - and I already have a fix. Alas, I'm not familiar with the branching/merging technique of GitHub --- how do I push a fix, and how do I have it reviewed by the owner, and how do I become a "contributor" ???