Hi!

Thank for this great project.

I'm connecting into the proxy using a python client and can manage to exchange a few messages successfully.
I'm getting this error after sending a ChannelRing to a channel:

"panic: runtime error: invalid memory address or nil pointer dereference" error

The ChannelRing is executed successfully, but this error appear right after and the proxy process crashes.

ari-proxy_1 | t=2020-03-30T18:55:14+0000 lvl=info msg="starting ari-proxy server" version=5.0.1 ari-proxy_1 | t=2020-03-30T18:55:18+0000 lvl=warn msg="failed to publish NATS message" subject= data="&{Error: Data:<nil> Key:<nil> Keys:[]}" error="nats: invalid subject" ari-proxy_1 | panic: runtime error: invalid memory address or nil pointer dereference ari-proxy_1 | [signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x867b53] ari-proxy_1 | ari-proxy_1 | goroutine 45 [running]: ari-proxy_1 | github.com/CyCoreSystems/ari-proxy/v5/server.(*Server).dialogsForEvent(0xc00009c500, 0xb77140, 0xc0001be100, 0xa3cfc0, 0xc0001be100, 0xc0000266f0) ari-proxy_1 | /home/travis/gopath/src/github.com/CyCoreSystems/ari-proxy/server/events.go:7 +0x113 ari-proxy_1 | github.com/CyCoreSystems/ari-proxy/v5/server.(*Server).runEventHandler(0xc00009c500, 0xb72a40, 0xc00005fb80) ari-proxy_1 | /home/travis/gopath/src/github.com/CyCoreSystems/ari-proxy/server/server.go:276 +0x51d ari-proxy_1 | created by github.com/CyCoreSystems/ari-proxy/v5/server.(*Server).listen ari-proxy_1 | /home/travis/gopath/src/github.com/CyCoreSystems/ari-proxy/server/server.go:221 +0x138e vagrant_ari-proxy_1 exited with code 2