When pressing enter at the end of a heading, we want to insert an empty paragraph instead of a new heading. This failed when the paragraph had a zero-width space in it because we didn't recognize it as empty. closes odoo/odoo#116558 X-original-commit: 228e7937f818f5606601e575b1d9a2bb87cda99d Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>