According to documentation j.l.i.MethodHandles.whileLoop(MethodHandle, MethodHandle, MethodHandle), 'init' might be null:

Passing null init function will make the loop's result type void.

Attached code provides example which throws IndexOutOfBoundsException; java.lang.IndexOutOfBoundsException: toIndex = 1
According to MethodHandles.loop(MethodHandle[]...), IllegalArgumentException should be thrown.

Was found on jdk9b107, tests are in development, tck_red label will be added after tests development completion.