Just doing a "list" command followed by a "pm xxxxxx" crashed the bridge with a panic. After the restart of the bridge the command worked. See the log part attached:
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: [Mar 21, 2019 15:19:45] [Command handler/DEBUG] Importing [email protected] for &{0xc000226460 0xc0002d40e0 0xc00009b9a0 0xc0002277c0 false true}
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: panic: runtime error: invalid memory address or nil pointer dereference
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: [signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x788fee]
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: goroutine 2691 [running]:
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: github.com/Rhymen/go-whatsapp.(*Conn).write(0xc0001be0a0, 0x1, 0xc003ef6710, 0x10, 0xc00044e140, 0x4a, 0x50, 0xc0001f2380, 0x7f4f366eed98, 0x0)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/pkg/mod/github.com/!rhymen/[email protected]/write.go:91 +0x3e
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: github.com/Rhymen/go-whatsapp.(*Conn).writeJson(0xc0001be0a0, 0xc002ab0540, 0x3, 0x3, 0x100000000000099, 0x0, 0xa)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/pkg/mod/github.com/!rhymen/[email protected]/write.go:27 +0x2c7
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: github.com/Rhymen/go-whatsapp.(*Conn).GetProfilePicThumb(...)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/pkg/mod/github.com/!rhymen/[email protected]/contact.go:25
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: maunium.net/go/mautrix-whatsapp/whatsapp-ext.(*ExtendedConn).GetProfilePicThumb(0xc0002d40e0, 0xc002966580, 0x1b, 0x0, 0xc00010a8c0, 0xa)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/mautrix-whatsapp/whatsapp-ext/whatsapp.go:121 +0x101
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: main.(*Puppet).UpdateAvatar(0xc0035fe320, 0xc000228a80, 0x0, 0x1)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/mautrix-whatsapp/puppet.go:132 +0x71d
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: main.(*Puppet).Sync(0xc0035fe320, 0xc000228a80, 0xc00050b4a0, 0x1b, 0xc0001a237a, 0x5, 0x0, 0x0, 0x0, 0x0)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/mautrix-whatsapp/puppet.go:194 +0x290
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: main.(*CommandHandler).CommandPM(0xc0001a5ea0, 0xc003451ef8)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/mautrix-whatsapp/commands.go:277 +0x41d
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: main.(*CommandHandler).Handle(0xc0001a5ea0, 0xc002954880, 0x1e, 0xc000228a80, 0xc003d723e0, 0xf)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/mautrix-whatsapp/commands.go:101 +0x20b
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: main.(*MatrixHandler).HandleMessage(0xc0001accc0, 0xc000590240)
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/mautrix-whatsapp/matrix.go:161 +0x203
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: created by maunium.net/go/mautrix-appservice.(*EventProcessor).Start
Mar 21 15:19:45 fblchat mautrix-whatsapp[14915]: #011/opt/golang/pkg/mod/maunium.net/go/[email protected]/eventprocessor.go:62 +0x55
Mar 21 15:19:45 fblchat systemd[1]: whatsapp-bridge.service: Main process exited, code=exited, status=2/INVALIDARGUMENT
Mar 21 15:19:45 fblchat systemd[1]: whatsapp-bridge.service: Unit entered failed state.
Mar 21 15:19:45 fblchat systemd[1]: whatsapp-bridge.service: Failed with result 'exit-code'.