Only if i use sipping with -c a request is generated

If I'm using sipping without -c it isn't generating a request.
-c is not used in delivered examples
also it isn't mentioned in help that -c is mandatory.

ubuntu@provider-instance-ubuntu-xxx:~/SIPPing-master$ ./sipping.py -r examples/register.txt -V -d 217.xxx.xxx.xxx -vuser:testuser -v .callid:"''.join(random.choice(string.ascii_lowercase + string.digits) for x in range(6))" -m string -m random -i 3 -S 80.xxx.xxx.xx
=======================================
I'm using these variables in templates:
=======================================
user: testuser
.callid: ''.join(random.choice(string.ascii_lowercase + string.digits) for x in range(6))
source_port: 5060
dest_ip: 217.xxx.xxx.xxx
source_ip: 80.xx.xx.xx
dest_port: 5060
=======================================

^C

statistics ---
Traceback (most recent call last):
File "./sipping.py", line 434, in
main()
File "./sipping.py", line 430, in main
sys.stderr.write('%d packets transmitted, %d packets received, %.1f%% packet loss\n' % (sent, rcvd, (float(sent - rcvd) / sent) * 100))
ZeroDivisionError: float division by zero

If im adding -c 1 it is generating a request

ubuntu@provider-instance-ubuntu-xxxx:~/SIPPing-master$ ./sipping.py -r examples/register.txt -V -d 217.xxx.xxx.xxx -vuser:testuser -v .callid:"''.join(random.choice(string.ascii_lowercase + string.digits) for x in range(6))" -m string -m random -i 3 -c 1 -S 80.xxx.xxx.xx
=======================================
I'm using these variables in templates:
=======================================
user: testuser
.callid: ''.join(random.choice(string.ascii_lowercase + string.digits) for x in range(6))
source_port: 5060
dest_ip: 217.xxx.xxx.xxx
source_ip: 80.xxxx.xxx.xx
dest_port: 5060
=======================================

sent

Request REGISTER to 217.xxx.xxx.xxx:5060 cseq=0 len=408

=== Full Request sent ===

REGISTER sip:217.xxx.xxx.xxx SIP/2.0
Content-Length: 0
Via: SIP/2.0/UDP 80.xxx.xxx.xx:5060;branch=z9hG4bK-p985iy;rport
From: "fake" sip:fake@80.xxx.xxx.xx;tag=as2e95fad1
Supported: path, outbound, gruu
Expires: 3600
User-Agent: SIPPing fake UA
To: sip:testuser@217.xxx.xxx.xxx:5060;line=kutixubf
Contact: sip:fake@80.xxx.xxx.xx:5060
CSeq: 0 REGISTER
Call-ID: jdf23g@fake
Max-Forwards: 70

SIP/2.0 403 Forbidden 11020021403
Content-Length: 0
Via: SIP/2.0/UDP 80.xxx.xxx.xx:5060;received=80.xxx.xxx.xx;rport=5060;branch=z9hG4bK-p985iy
From: "fake" sip:fake@80.xxx.xxx.xx;tag=as2e95fad1
Service-Route: sip:217.xxx.xxx.xxx:5060;transport=udp;lr
To: sip:testuser@217.xxx.xxx.xxx;line=kutixubf;tag=h7g4Esbg_889a74220b775780cd862d6b1ebe2a
CSeq: 0 REGISTER
Call-ID: jdf23g@fake
Path: sip:217.xxx.xxx.xxx;transport=udp;lr;ob

received Response 403 Forbidden 11020021403 from 217.xxx.xxx.xxx:5060 cseq=0

--- statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss