anchor.diff:    Result := TNullableDateTime.VariantToString(Self.AsVariant, aShowTime);
   end;
   
  +function TNullableDateTime.AsString: String;
  +begin
  +  Result := AsString(true);
  +end;
  +
   { TAbstractNullable }
   
   function TAbstractNullable.GetNotNull: Boolean;
  
positive.code:       class function StringToVariant(const aValue : String): Variant;
        class function VariantToString(const aValue: Variant; const aShowTime: boolean): String;
  
        function AsString (const aShowTime : boolean) : String;
  
        property Value : TDateTime read GetValue write SetValue;
    end;
  
negative.code:     procedure Assign(const aValue: variant); overload; virtual; abstract;
  
      function CheckIfDifferentAndAssign(const aValue : Variant) : boolean; virtual; abstract;
      function AsString: String; virtual; abstract;
  
      property IsNull: Boolean read FIsNull write FIsNull;
      property NotNull: Boolean read GetNotNull;
  