[Tim Wood]

You'll need to mirror or use directly the build settings in OmniGroup/Configurations/Touch-Application-*.xcconfig. We put our common configuration settings in these files and then reference them from our application build styles (for an example, see the build settings for the TextEditor project and target in OmniGroup/Frameworks/OmniUI/iPad/Examples.

For this particular issue, the build settings you need specifically are from here:

./Touch-Application-Common.xcconfig:OTHER_LDFLAGS = $(value) -all_load -ObjC

This tells the linker to bring in the Objective-C category symbols from the static libraries you've included already. By default, these aren't included since they aren't referenced directly. The -isNull method is a category method on NSObject, defined in OmniFoundation's OFNull.[hm].