As happening with empty dummy ".class" / empty.jar files in tests
for example during:
 JavaElementDeltaTests.testChangeExternalLibFolder3(),
 CompletionTests2.testBug281598b().
Empty files are no real problem they just do not need to be indexed.

was ArrayIndexOutOfBoundsException / "java.util.zip.ZipException: zip
file is empty" with long stacktraces flooding the logfile