panic in main.discovery(...)

[SpComb]

INFO                 heads:events                         update
INFO                                                      artnet.Discovery: 192.168.2.134:6454:
INFO                                                            Name: qmsk-esp-520358
INFO                                                            Ports: input=0 output=1
INFO                                                            Output 0: 0:0.7
INFO                 heads:events                         update
INFO                                                      artnet.Discovery: 192.168.2.131:6454:
INFO                                                            Name: qmsk-esp-c94b30
INFO                                                            Ports: input=0 output=1
INFO                                                            Output 0: 0:2.1
INFO                 heads:events                         update
INFO                                                      artnet.Discovery: 192.168.2.118:6454:
INFO                                                            Name: qmsk-esp-5f98ed
INFO                                                            Ports: input=0 output=1
INFO                                                            Output 0: 0:1.1
INFO                 heads:events                         update
INFO                                                      artnet.Discovery: 192.168.2.130:6454:
INFO                                                            Name: qmsk-esp-fabd8c
INFO                                                            Ports: input=0 output=1
INFO                                                            Output 0: 0:3.0
INFO                 heads:events                         update
INFO                                                      artnet.Discovery: 192.168.2.120:6454:
INFO                                                            Name: qmsk-esp-7567e8
INFO                                                            Ports: input=0 output=2
INFO                                                            Output 0: 0:2.3
INFO                 heads:events                         update
INFO                                                            Output 1: 0:2.4
INFO                 heads:events                         update
INFO                                                      artnet.Discovery: 192.168.2.134:6454:
INFO                                                            Name: qmsk-esp-520358
INFO                                                            Ports: input=0 output=1
INFO                                                            Output 0: 0:0.7
INFO                 heads:events                         update
INFO                                                      artnet.Discovery: 192.168.2.131:6454:
INFO                                                            Name: qmsk-esp-c94b30
INFO                                                            Ports: input=1 output=1
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x3 pc=0x6ffc71]
goroutine 5 [running]:
main.discovery(0xc4200a42c0, 0xc4200f9a40)
        /go/src/github.com/qmsk/dmx/cmd/qmsk-dmx/main.go:43 +0x121
created by main.main
        /go/src/github.com/qmsk/dmx/cmd/qmsk-dmx/main.go:149 +0x303
qmsk-dmx.service: Main process exited, code=exited, status=2/INVALIDARGUMENT