Unable to build UE4 or AR Sample schemes on OSX 10.12.5

I am trying to build the ARKit samples. I followed the documentation on the github to build all threes schemes in order. The first two work successfully, but when I try to build hte ARKit sample or the UE4 scheme I get the following error in a few different locations:

Nullability specifier '_Nullable' conflicts with existing specifier '_Nonnull'

Yes Admiral, this seems to be a problem since Xcode beta 3 (and 4).
I have the same problem. It seems the Xcode beta 2 does not have this problem. You will find more info and a download link at the following location: