augroup help_versions
  autocmd! FileType vim,help call helpful#setup()
augroup END

command! -nargs=+ -complete=help HelpfulVersion call helpful#lookup('<args>')

augroup help_versions
  autocmd! FileType vim,help call helpful#setup()
augroup END

command! -nargs=+ -complete=help HelpfulVersion call helpful#lookup(<q-args>)

Use <q-args> instead of '<args>'
Use <q-args> instead of '<args>'

Give an option name surrounded with "'" to a command argument like
`:HelpfulVersion 'shiftwidth'` didn't work.

tweekmonster/helpful.vim