Java doesn't allow you to have null as an attribute value. It wants you to indicate what you really mean by null, so that is what we do here - as ugly as it is.
| Modifiers | Name | Description | 
|---|---|---|
static class  | 
                            Undefined.CLASS | 
                            |
static class  | 
                            Undefined.EXCEPTION | 
                            
| Type Params | Return Type | Name and description | 
|---|---|---|
 | 
                            static boolean | 
                            isUndefined(String other) | 
                        
 | 
                            static boolean | 
                            isUndefined(ClassNode other) | 
                        
 | 
                            static boolean | 
                            isUndefinedException(ClassNode other) |