@miconda indeed you are right, but it will help in this situation: - first request has not SOME_HEADER - try to use a $var which value has not been explicitly set before => log a warning
If we start kamailio with e.g. 64 (routing) child processes there are 64 first SIP messages that might or might not have SOME_HEADER => some will print warning, some will not => if really unlucky, all will not :D