58d3b670221b3 was not correctly forward ported, it misses the `''` fallback part
of the original commit dc20ab9c02
Without this, traceback is shown.
Step to reproduce:
- Open HTML Editor (or edit a backend view)
- Add an input with no class but a value attribute (no type or type text)
closes odoo/odoo#73057
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>