Problem to add new values ​​to a bigintList field

Problem to add new values ​​to a bigintList field

Hi. I have a problem adding new records to a multiple search field "Bigint list". I use the method list.add (value) but then it does not work, for this I have to convert to string, add "," + new value and then revert to list before assigning it to the corresponding "bigint list" field .. I do not think it works properly, but that's how it works. My question is .. can the new value be added simply by using the "add (value)" method? Since I think part of that when I create a new record in a form, I want that ID of this new record to be added to another record by using the multiple search field (bigint list). Idea example:

On success In form BASE

idFormA = insert into FormA [ <field> = <expression> <field> = <expression> <field> = <expression> ];

formB =  FormB [Name == BASE.Name  ];

formB.fieldBigIntList.add( idFormA.toLong() );


It does not give an error but it does not work.
Neither with the value as toString () nor without toLong ()


Any help please? Thank you.