Using openjfx and binary stub from jdkb100
cd rt
gradle -PBINARY_STUB=/home/user/jdkb100/jfxrt.jar

fails with:
* Where:
Build file '/home/tb115823/work/openjfx/rt/build.gradle' line: 2224
* What went wrong:
Execution failed for task ':web:copyClassesFromBinaryStub'.
> No signature of method: java.lang.String.getSingleFile() is applicable for argument types: () values: []



If you look at line 2224 BINARY_STUB property probably isn't FileCollection.