Same kind of error here. Temporarily solved by using tag v3.37 (assumed previous version). So my Repository line now reads: "qmcgaw/gluetun:v3.37".
Same issue seems to be reported on GItHub as well.
2024-03-19T06:46:49+02:00 INFO [http server] http server listening on [::]:8000
2024-03-19T06:46:49+02:00 INFO [healthcheck] listening on 127.0.0.1:9999
2024-03-19T06:46:49+02:00 INFO [dns] using plaintext DNS at address 1.1.1.1
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x78e831]
goroutine 119 [running]:
github.com/qdm12/gluetun/internal/storage.filterServer({{0xc0027464c0, 0x9}, {0xc0027464c9, 0x7}, {0x0, 0x0}, {0xc0027465c0, 0x6}, {0xc0027465c6, 0x9}, ...}, ...)
github.com/qdm12/gluetun/internal/storage/filter.go:77 +0x1b1
github.com/qdm12/gluetun/internal/storage.(*Storage).FilterServers(_, {_, _}, {{0xc0000281e9, 0x9}, {{0x0, 0xffff00000000}, 0xc000010018}, {0xc0002621b0, 0x9, ...}, ...})
github.com/qdm12/gluetun/internal/storage/filter.go:33 +0x2fb
github.com/qdm12/gluetun/internal/provider/utils.GetConnection({_, _}, {_, _}, {{0xc0000281e9, 0x9}, {{0x0, 0xffff00000000}, 0xc000010018}, {0xc0002621b0, ...}, ...}, ...)
github.com/qdm12/gluetun/internal/provider/utils/connection.go:39 +0xad
github.com/qdm12/gluetun/internal/provider/mullvad.(*Provider).GetConnection(_, {{0xc0000281e9, 0x9}, {{0x0, 0xffff00000000}, 0xc000010018}, {0xc0002621b0, 0x9, 0x9}, {0x0, ...}, ...}, ...)
github.com/qdm12/gluetun/internal/provider/mullvad/connection.go:12 +0x105
github.com/qdm12/gluetun/internal/vpn.setupWireguard({_, _}, {_, _}, {_, _}, {_, _}, {{0xc0000281e9, 0x9}, ...}, ...)
github.com/qdm12/gluetun/internal/vpn/wireguard.go:20 +0xbe
github.com/qdm12/gluetun/internal/vpn.(*Loop).Run(0xc000238420, {0x109d840, 0xc0002663c0}, 0xc0002567e0?)
github.com/qdm12/gluetun/internal/vpn/run.go:40 +0x4f5
created by main._main in goroutine 14
./main.go:427 +0x385a