With commit that replaced most of the text fields to HTML fields (see commit[1]), the `description_to_html_lines` method was removed from `calendar.event` model and linked templates. But another commit[2] merged afterwards introduced a mail template that used this method, due to which the rendering used to crashed. This commit adapts the template and thus fixes the crash while rendering the template. commit[1] - https://github.com/odoo/odoo/commit/cb4f597410bcb08208ee277144d755bef8b6d688 commit[2] - https://github.com/odoo/odoo/commit/40fd44f618cb54d8c75b8c090cc36655316aa825 task-2821957 closes odoo/odoo#91280 X-original-commit: 71b9e36f5c5e36f13f26bf74038ddb736d5e25de Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>