commit https://github.com/vim/vim/commit/385111bd86e0b38667879c3e89506ca1ae98e1df Author: Bram Moolenaar <Bram@vim.org> Date: Sat Mar 12 19:23:00 2016 +0100 patch 7.4.1547 Problem: Getting a cterm highlight attribute that is not set results in the string "-1". Solution: Return an empty string. (Taro Muraoka)

" 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