The spec says that the method isLeapYear(long prolepticYear) accepts as parameter prolepticYear which is not validated for range.
http://docs.oracle.com/javase/8/docs/api/java/time/chrono/HijrahChronology.html#isLeapYear-long-
But f.e. in the case of using one of the following values 1004, 1008, 1012, 2000, 400, 4, 400000000, 0, 96, -4, -400000000 as parameter the unexpected DateTimeException is thrown:
java.time.DateTimeException: Hijrah date out of range
Tests belonging to the JCK9 suite (not yet integrated) will fail due to this issue: api/java_time/chrono/HijrahChronology/index.html#IsLeapYear
(not integrated yet)