Prior to this commit, if a single null value was passed to a method with
a varargs array of type java.util.Optional, that null value was passed
unmodified. On the contrary, a null passed with additional values to
such a method resulted in the null being converted to Optional.empty().
This commit ensures that a single null value is also converted to
Optional.empty() for such SpEL expressions.
Closes gh-27795
b2e94f611f