completion.lua:253: bad argument #1 to 'len' (string expected, got nil)

[RonanMacF]

My testing minimal init.vim

lua << EOF
  require'completion'.on_attach()
EOF

plugins are installed through nix home-manager

How to reproduce start neovim see error E5108: Error executing lua ...ck/home-manager/start/completion-nvim/lua/completion.lua:253: bad argument #1 to 'len' (string expected, got nil)

Expected behavior no error

[RonanMacF]

this can easily by fixed by just setting let g:completion_confirm_key = "\<C-y>" but I would have expected this to not be required as there is supposed to be defaut.