problem with `getInitialState` returning `null`

[chenglou]

Right now it's accepted to return null from getInitialState, but if a mixin also defines a getInitialState, and if one of the two returns null then the merge throws an error when trying to merge an object with null. What should be the correct behavior here?

@cpojer

[syranide]

#725

Perhaps we have a good reason to not allow null then.

[syranide]

Can't test right now, but is this perhaps a problem with style too? I'm assuming they use the same helper?