Phone being always 486 Busy when it has incoming call

[I3ootman]

I tried making basic phone (my own, not taken from example). Two phones then connect via Asterisk server. If Phone 2 calls Phone 1 it always gets 486 Busy. I dug into code of VoIP file and found that upon recieving sip.INVITE VoIPPhone.callback() calls _callback_MSG_Invite() where it recieves this INVITE message and should call _createCall().

But if you inspect _callback_MSG_Invite() closely you can see these lines:
if self.callCallback is None: message = self.sip.gen_busy(request) self.sip.out.sendto( message.encode("utf8"), (self.server, self.port) )
[line 564-568]

If self.callCallback is None then it calls sip.gen_busy() but the problem is self.callCallback is always None as i can see cuz callback() does not return anything.
On the other hand there is a note in documentation that says:
"This function [callback()] then creates a VoIPCall or terminates it respectively. When a VoIPCall is created, it will then pass it to the callCallback function as an argument. If callCallback is set to None, this function replies as BUSY."

That means that VoIPCall object should be created before this check but it actually created after the None check in code. @tayler6000 explain please how do i handle this situation or is it a kinda bug?

[I3ootman]

I opened VoIP file in my project and commented this check on line 564. After that call actually got accepted.