public class AmbiguousCall
{
	public static void foo (Integer i) {}
	public static void foo (String s) {}

	public static void main (String[] args)
	{
		foo(null);
		foo((String)null); // ok
	}
}

/* Error message:

AmbiguousCall.java:8: reference to foo is ambiguous, both method foo(java.lang.Integer) in AmbiguousCall and method foo(java.lang.String) in AmbiguousCall match
                foo(null);
                ^
1 error
*/