anchor.diff:    if VarIsNull(aValue) then
     begin
       Result := not IsNull;
  -    Self.IsNull:= true
  +    CreateAsNull;
     end
     else
     begin
  
positive.code:     function AsString : String;
    end;
  
  
  implementation
  
  uses
    SysUtils {$IFDEF FPC}, LazUtf8{$ENDIF};
  
  { TNullableStringRecord }
  
  procedure TNullableStringRecord.CreateAsNull;
  
negative.code: procedure TNullableStringRecord.Assign(aSourceField: TField);
  begin
    if aSourceField.IsNull then
      CreateAsNull
    else
      CreateWithValue(aSourceField.AsString);
  end;
  
  procedure TNullableStringRecord.Assign(const aValue: String);
  