Method Collections.nCopies() returns List spliterator of which is expected to be ORDERED.
This is not so in the case of an empty list.
Consider the following code:

        boolean ordered = Collections.nCopies(0, new Object()).spliterator().hasCharacteristics(Spliterator.ORDERED);
        System.out.println("ordered = " + ordered);
 

The output will be:

ordered = false


The following JCK tests will fail due to this:

api/java_util/Collections/ncopies/index.html#NCopiesSpliteratorEmpty[characteristics_ORDERED]
api/java_util/Collections/ncopies/index.html#NCopiesSpliteratorEmpty[forEachRemaining_NPE]
api/java_util/Collections/ncopies/index.html#NCopiesSpliteratorEmpty[hasCharacteristics_ORDERED]
api/java_util/Collections/ncopies/index.html#NCopiesSpliteratorEmpty[tryAdvance_NPE]
api/java_util/Collections/ncopies/index.html#NCopiesStream[checkSpliterator]
api/java_util/Collections/ncopies/index.html#NCopiesParallelStream[checkSpliterator]