zsh sqlcmd completion is broken

Installed sqlcmd on MacOS with HomeBrew. After rebuilding ~/.zcompdump the command shows up fine:

% cat ~/.zcompdump | rg sqlcmd
'sqlcmd' '_sqlcmd'

However, trying to autocomplete commands like sqlcmd conf<TAB> or plain sqlcmd <TAB> does nothing.

Looks like there's a real problem there:

~ % sqlcmd __complete ''
panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
github.com/microsoft/go-sqlcmd/cmd/sqlcmd.isFlag(...)
        github.com/microsoft/go-sqlcmd/cmd/sqlcmd/sqlcmd.go:375
github.com/microsoft/go-sqlcmd/cmd/sqlcmd.checkDefaultValue({0x13c831621600, 0x2, 0x13c8317add88?}, 0x1)
        github.com/microsoft/go-sqlcmd/cmd/sqlcmd/sqlcmd.go:362 +0x2b8
github.com/microsoft/go-sqlcmd/cmd/sqlcmd.convertOsArgs({0x13c8312b6310?, 0x101b82380?, 0x100e1cb4b?})
        github.com/microsoft/go-sqlcmd/cmd/sqlcmd/sqlcmd.go:319 +0x1f0
github.com/microsoft/go-sqlcmd/cmd/sqlcmd.Execute({0x1010ea180, 0x6})
        github.com/microsoft/go-sqlcmd/cmd/sqlcmd/sqlcmd.go:289 +0x148
main.main()
        github.com/microsoft/go-sqlcmd/cmd/modern/main.go:52 +0x1b4

~ % sqlcmd __complete conf
:0
Completion ended with directive: ShellCompDirectiveDefault

Version: sqlcmd ✔: stable 1.10.0 (bottled)

Reproduce the failure with sqlcmd __complete '' and sqlcmd __complete conf, then read the completion argument path in cmd/sqlcmd/sqlcmd.go around lines 289, 319, 362, and 375, along with cmd/modern/main.go:52. Done means zsh completion for sqlcmd produces suggestions for commands and an empty prompt without panicking.