Plugin stops working in Gradle 2.12
Gradle team recently published Gradle 2.12 RC. An user reported an issue with clojuresque at https://discuss.gradle.org/t/gradle-2-12-rc-1-is-now-available-for-testing/15006/7.
This is due to a change in Gradle's internal API made in this commit https://github.com/gradle/gradle/commit/4e5e9fba8cb2456b191a1365d786e914b2526a7b.
Preferably the plugin should not use Gradle's internal API as it might change between releases without prior notice. A quick fix would be to just pass an instance of DefaultDirectoryFileTreeFactory to the DefaultSourceDirectorySet constructor.