When building with Gradle 2.12 I get the following error:

* Where:
Build file '/Users/scott/dev/OpenJFX9-dev/build.gradle' line: 128

* What went wrong:
Could not compile build file '/Users/scott/dev/OpenJFX9-dev/build.gradle'.
> startup failed:
  build file '/Users/scott/dev/OpenJFX9-dev/build.gradle': 128: unable to resolve class Map.Entry
   @ line 128, column 9.
             for (Map.Entry property in config) {
             ^
  
  1 error

The fix is to use the fully-qualified class name for java.util.Map.Entry (importing java.util.Map does not work).

With this change Gradle 2.12 appears to work properly for building.
The same problem exists in the 8u-dev repo.