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Kotlin only robolectric_test targets fail to compile

See original GitHub issue

The following error appears when trying to compile a robolectric_test target that contains only kotlin code:

2017-08-28 17:07:31.143][error][command:null][tid:217][com.facebook.buck.cli.Main] Uncaught exception at top level
java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.RuntimeException: Building rule [//features/check-balance:test_debug#testsjar] failed. Caused by [NoSuchFileException]:
/Users/cwoodward/Development/project/buck-out/gen/features/check-balance/lib__test_debug#testsjar__output/used-classes.json
    at com.facebook.buck.command.Build.executeAndPrintFailuresToEventBus(Build.java:332)
    at com.facebook.buck.cli.TestCommand.runWithoutHelp(TestCommand.java:548)
    at com.facebook.buck.cli.AbstractCommand.run(AbstractCommand.java:227)
    at com.facebook.buck.cli.AbstractContainerCommand.run(AbstractContainerCommand.java:67)
    at com.facebook.buck.cli.BuckCommand.run(BuckCommand.java:81)
    at com.facebook.buck.cli.Main.runMainWithExitCode(Main.java:984)
    at com.facebook.buck.cli.Main.runMainThenExit(Main.java:371)
    at com.facebook.buck.cli.Main.nailMain(Main.java:1729)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.martiansoftware.nailgun.NGSession.run(NGSession.java:329)

My guess is because there is no java, it is missing the used-classes.json file. Test targets that contain mixed java + kotlin do not have this issue.