Neovim 0.10 Compatible Functions Require a Default

[cenk1cenk2]

Thank you for maintaining this beautiful plugin. With the latest changes I have encountered a tiny bit of error therefore I have opened up this merge request.

It throws errors when the configured formater does not have a default.

   Error  11:10:56 msg_show.lua_error Error detected while processing BufWritePre Autocommands for "*":
11:10:56 msg_show Error executing lua callback: vim/shared.lua:0: src: expected table, got nil
stack traceback:
    [C]: in function 'error'
    vim/shared.lua: in function 'validate'
    vim/shared.lua: in function 'list_extend'
    ....local/share/nvim/lazy/conform.nvim/lua/conform/util.lua:142: in function 'computed_args'
    ...ocal/share/nvim/lazy/conform.nvim/lua/conform/runner.lua:29: in function 'build_cmd'
    ...ocal/share/nvim/lazy/conform.nvim/lua/conform/runner.lua:280: in function 'run_formatter'
    ...ocal/share/nvim/lazy/conform.nvim/lua/conform/runner.lua:622: in function 'format_lines_sync'
    ...ocal/share/nvim/lazy/conform.nvim/lua/conform/runner.lua:578: in function 'format_sync'
    ....local/share/nvim/lazy/conform.nvim/lua/conform/init.lua:451: in function 'format'
    /Users/cenk/.config/nvim/lua/extensions/conform-nvim.lua:85: in function 'format'
    /Users/cenk/.config/nvim/lua/lvim/lsp/format.lua:10: in function </Users/cenk/.config/nvim/lua/lvim/lsp/format.lua:9>

[stevearc]

Thanks for the PR!