If you try to cast a reference type (complex type whatever you wanna call it) to a bool, implicit cast (if it's even a cast at this point) works fine while explicit cast throws some nonsense error.

class MyType { }
void MyFn() {
  MyType myType;
  bool isNull1 = myType;
  bool isNull2 = (bool)myType; // throws error, "Can't find variable 'myType'" wat?
}