This avoids the following warning:
../plugins/sip/calls-sip-origin.c: In function ‘sip_r_register’:
../plugins/sip/calls-sip-origin.c:483:26: warning: the comparison will always evaluate as ‘true’ for the address of ‘m_url’ will never be NULL [-Waddress]
483 | if (sip->sip_contact && sip->sip_contact->m_url && sip->sip_contact->m_url->url_host) {
| ^~
In file included from /usr/include/sofia-sip-1.12/sofia-sip/nua.h:47,
from ../plugins/sip/calls-sip-util.h:28,
from ../plugins/sip/calls-sip-call.h:30,
from ../plugins/sip/calls-sip-origin.c:31:
/usr/include/sofia-sip-1.12/sofia-sip/sip.h:477:23: note: ‘m_url’ declared here
477 | url_t m_url[1]; /**< SIP URL */
| ^~~~~
../plugins/sip/calls-sip-origin.c: In function ‘sip_callback’:
../plugins/sip/calls-sip-origin.c:779:23: warning: the comparison will always evaluate as ‘true’ for the address of ‘a_url’ will never be NULL [-Waddress]
779 | if (sip->sip_from && sip->sip_from->a_url &&
| ^~
/usr/include/sofia-sip-1.12/sofia-sip/sip.h:386:22: note: ‘a_url’ declared here
386 | url_t a_url[1]; /**< URL */
| ^~~~~
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