anchor.diff:      procedure Assign(aSourceField : TField); override; overload;
       procedure Assign (const aValue : Variant); override; overload;
       procedure Assign (const aValue : string); override; overload;
  +
  +    function CheckIfDifferentAndAssign(const aValue : Variant) : boolean; override;
       function AsVariant: Variant; override;
   
       class function StringToVariant(const aValue: String): Variant;
  
positive.code:   Self.Assign(aValue);
    if aAllowBlankValue then
      Self.ChangeToBlankIfNull;
  end;
  
  function TNullableString.CheckIfDifferentAndAssign(const aValue: Variant): boolean;
  
negative.code:     if Result then
        Self.Value:= tmpDate;
    end;
    Self.FTagChanged:= Result;
  end;
  
  class function TNullableDateTime.StringToVariant(const aValue: String): Variant;
  