[FIX] link_tracker,test_mail_full: fix traceback while converting links

Currently, when we try to shorten the links from content with help of
`_shorten_links_text` method, it throws traceback if the body(content)
we pass is `False`(might happen when we directly pass a model field of
textual type but the field doesn't have a value yet). It's because
the `re` expects the content to be string / bytestring.

This commit fixes the issue by adding a check in this method, which
will simply return `False` if there's no body.

Task-2628586

closes odoo/odoo#75987

X-original-commit: 41f59a61
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/link_tracker/models/mail_render_mixin.py

@@ -55,6 +55,8 @@ class MailRenderMixin(models.AbstractModel):
 
         :return: updated content
         """
+        if not content:
+            return content
         base_url = base_url or self.env['ir.config_parameter'].sudo().get_param('web.base.url')
         shortened_schema = base_url + '/r/'
         unsubscribe_schema = base_url + '/sms/'

addons/test_mail_full/tests/test_sms_sms.py

@@ -82,6 +82,9 @@ class TestSMSPost(TestMailFullCommon, LinkTrackerMock):
         })
         link = self.env['link.tracker'].search([('url', '=', link)])
         self.assertIn(link.short_url, new_body)
+        # Bugfix: ensure void content convert does not crash
+        new_body = self.env['mail.render.mixin']._shorten_links_text(False, self.tracker_values)
+        self.assertFalse(new_body)
 
     def test_body_link_shorten_wshort(self):
         link = 'https://test.odoo.com/r/RAOUL'