FilePath folder lookup does not work. Why?

There is a new field on our table. Field bases on Extended Data Type FilePath.

This fields has been added to a form. We can see an automatic lookup button. It looks like a folder button.

The issue is, that this folder button does not work. We can click on it, but there is no new window when we can choose a folder to store files.

The "magic trick" is, that we have to add to method node of our form new method
Metod name is filePathLookupTitle

This method returns some string.

Example

str filePathLookupTitle()
{
    // Archive directory
    return "@SYS26605";
}

The good example is on system form DocuType