The one-liner requirement is stupid.

LINQ is a dream here.

I think a failure on null is reasonable. In Java we have to assume that value are not null, since the alternative is an excessive number of checks. Optional exists for the cases where a value may be present or not.

Why not just check if the character is in range?

This is a slow solution. Why sort the array when you can just walk it?

The Java version needs this test:

Object[] haystack4 = {new StringBuilder().append("needle").toString()};

This is due to the Java compiler sharing String instances where possible, resulting in == being sufficient for the tests where .equals should really be used.

Be careful with this one! .equals should be used for string comparison.

Creating a Stack seems over the top!