setter property
      
      SetterElement?
      get
      setter
      
    
    
The setter associated with this variable.
Returns null if the variable is effectively final and therefore does
not have a setter associated with it.
This can happen either because the variable is explicitly defined as
being final or because the variable is induced by an explicit getter
that does not have a corresponding setter. If this variable was
explicitly defined (is not synthetic) then the setter associated with
it will be synthetic.
Implementation
SetterElement? get setter;