anchor.diff:      function AsString: String; override;
       function AsStringUseNumbers : String;
       function AsBoolean: Boolean;
  +    function ValueIsEqual (const aValue : Boolean) : boolean; overload;
  +    function ValueIsEqual (const aValue : TNullableBoolean) : boolean; overload;
   
       class function StringToVariant(const aValue: String): Variant;
       class function VariantToString(const aValue: Variant): String;
  
positive.code:   Result := (Self.NotNull) and (Self.Value);
  end;
  
  function TNullableBoolean.CheckIfDifferentAndAssign(const aValue: Variant): boolean;
  var
    tmpBool : boolean;
  
negative.code:     procedure Trim();
      procedure Uppercase();
      procedure ChangeToBlankIfNull;
      function ValueIsEqual (const aValue : String) : boolean; overload;
      function ValueIsEqual (const aValue : TNullableString) : boolean; overload;
      function ValueIsEqualCaseInsensitive (const aValue : String): boolean;
  
      class function StringToVariant(const aValue: String; const aAllowBlankValues : boolean): Variant;
      class function VariantToString(const aValue: Variant): String;
  