anchor.diff:    FValue := aValue;
   end;
   
  -procedure TNullableBoolean.Assign(aSource: TNullableBoolean);
  +procedure TNullableBoolean.Assign(const aSource: TNullableBoolean);
   begin
     if not aSource.IsNull then
       Self.Value := aSource.Value
  
positive.code:       constructor Create(); override; overload;
        constructor Create(aValue: TDateTime); overload;
  
        procedure Assign(aSource : TNullableDateTime); overload;
        procedure Assign(aSourceField : TField); override; overload;
        procedure Assign (const aValue: Variant); override; overload;
        procedure Assign (const aValue: String); override; overload;
        function AsVariant: Variant; override;
  
negative.code:     procedure CreateAsNull;
      procedure CreateWithValue (const aValue: Double);
  
      procedure Assign(const aSource : TNullableDoubleRecord); overload;
      procedure Assign(const aSourceField : TField); overload;
      procedure Assign(const aValue : String); overload;
      procedure Assign(const aValue : Variant);overload;
      function CheckIfDifferentAndAssign(const aValue : Variant) : boolean;
  