Next Gen HRHD custom field default

Hi,

Has anyone managed to get default expressions working for custom fields in Next Gen HRHD? I've attempted to use the following expression in a custom field of mine, to return the Primary Contact's person number, but it's not working. It's a text field, but I've also tried using a formula field which also didn't work. It's returning the word 'true' instead of populating the field with the person number.

Any advice would be much appreciated!

Field API name: CustomEmployeePersonNumberText_c

Default Value Expression:

def personnumbervalue = hcmPersonList?.first()?.PersonNumber;

setAttribute('CustomEmployeePersonNumberText_c',personnumbervalue);

return true;

Thanks,

-Edward