gradle not supported?

[Jesse Gibbons]

I noticed when I search the code for gradle I get
- code deleting the provided gradle jar
- comments about keeping a version of two different packages back
  because they require gradle. 

I'm guessing the gradle jar is deleted because it isn't compiled for
guix. But why are these packages (java-htsjdk and java-picard in
gnu/packages/bioinformatics.scm) held back to not depend on gradle?

If I need a package that uses gradlew to build, what is the best
solution for defining it?

Thanks,
-Jesse