commit https://github.com/vim/vim/commit/7a5c46a9df7ef01a4f6a620861c35400d5ad28d9 Author: Bram Moolenaar <Bram@vim.org> Date: Wed Mar 16 20:41:21 2016 +0100 patch 7.4.1580 Problem: Crash when using function reference. (Luchr) Solution: Set initial refcount. (Ken Takata, closes https://github.com/vim/vim/issues/690)

" Test for joining lines.

func Test_join_with_count()
  new
  call setline(1, ['one', 'two', 'three', 'four'])
  normal J
  call assert_equal('one two', getline(1))
  %del
  call setline(1, ['one', 'two', 'three', 'four'])
  normal 10J
  call assert_equal('one two three four', getline(1))
  quit!
endfunc