public static <T> Supplier<T> ifNull(Supplier<T> s) {
		return s == null ? supplier() : s;
	}
Returns the given callback object if it is not {@code null}.  Otherwise, a {@link #callback()}
is returned.  This is useful to avoid using {@code null}.

@param s the supplier function to check for {@code null}
@return a non-null supplier
Ghidra/Framework/Utility/src/main/java/utility/function/Dummy.java