anchor.diff:  begin
     if VarIsNull(aValue) then
     begin
  -    Result := Self.NotNull;
  +    Result:= Self.NotNull;
       Self.IsNull:= true
     end
     else
     begin
       if Self.IsNull then
  -      Result := true
  +      Result:= true
       else
  -      Result := aValue <> FValue;
  +      Result:= aValue <> FValue;
       if Result then
         Self.Value:= aValue;
     end;
  
positive.code: function TNullableString.GetValue: String;
  begin
    if (FIsNull) then
         Result := null
      else
        Result := FValue;
  end;
  
  procedure TNullableString.SetValue(AValue: String);
  begin
    FValue:= aValue;
    FIsNull := False;
  end;
  
  constructor TNullableString.Create();
  
negative.code: procedure TNullableString.Assign(aSource: TNullableString);
  begin
    if not aSource.IsNull then
      Self.Value:= aSource.Value
    else
      Self.IsNull:= true;
  end;
  
  procedure TNullableString.Assign(aSourceField: TField);
  