supertype property
      
      InterfaceType?
      get
      supertype
      
    
    
The superclass of this element.
For ClassElement returns null only if this class is Object. If the
superclass is not explicitly specified, or the superclass cannot be
resolved, then the implicit superclass Object is returned.
For EnumElement returns Enum from dart:core.
For MixinElement always returns null.
Note: Because the element model represents the state of the code, it is possible for it to be semantically invalid. In particular, it is not safe to assume that the inheritance structure of a class does not contain a cycle. Clients that traverse the inheritance structure must explicitly guard against infinite loops.
Implementation
InterfaceType? get supertype;