test: add missing helper function

redmail/test/helpers/convert.py

@@ -10,6 +10,9 @@ def remove_email_extra(s:str):
     s = remove_extra_lines(s)
     return s.replace("=20", "").replace('"3D', "").replace("=\n", "")
 
+def remove_email_content_id(s:str, repl="<ID>"):
+    return re.sub(r"(?<================)[0-9]+(?===)", repl, s)
+
 def payloads_to_dict(*parts):
     data = {}
     for part in parts:
@@ -25,6 +28,9 @@ def payloads_to_dict(*parts):
             key = new_key
         if isinstance(payload, str):
             data[key] = payload
+        elif payload is None:
+            # Most likely empty message
+            pass
         else:
             data[key] = payloads_to_dict(*payload)
     return data