Hi Dejan,
I see you are using a Buildship 2.x snapshot which is the work-in-progress version for the composite build support. The 2.x Buildship branch still uses an incubating Gradle API to access build configuration which was removed in Gradle 3.1. This will be fixed once the new API is in place.
In the meanwhile I suggest to use the stable 1.x releases. I’ll update this thread once we fixed this issue.