[FIX] re.search will return None when nothing found. So we have to check for this

mail_tracking/__manifest__.py

@@ -7,7 +7,7 @@
 {
     "name": "Email tracking",
     "summary": "Email tracking system for all mails sent",
-    "version": "13.0.1.0.4",
+    "version": "13.0.1.0.5",
     "category": "Social Network",
     "website": "http://github.com/OCA/social",
     "author": ("Tecnativa, " "Odoo Community Association (OCA)"),

mail_tracking/models/ir_mail_server.py

@@ -23,7 +23,7 @@ class IrMailServer(models.Model):
         body = body or ""
         # https://regex101.com/r/lW4cB1/2
         match = re.search(r'<img[^>]*data-odoo-tracking-email=["\']([0-9]*)["\']', body)
-        return int(match.group(1)) if match.group(1) else False
+        return int(match.group(1)) if match and match.group(1) else False
 
     def build_email(
         self,