Error when opening calendar and wiki list is empty

[emilsenan]

Error detected while processing function calendar#show[337]..vimwiki#diary#calendar_sign[6]..VimwikiGet:
line    3:
E684: list index out of range: 0
E116: Invalid arguments for function has_key(g:vimwiki_list[idx], a:option)
E15: Invalid expression: has_key(g:vimwiki_list[idx], a:option)

Steps to reproduce:

0. install Calendar.vim (https://github.com/mattn/calendar-vim)
1. let g:vimwiki_list = []
2. open vim
3. try to open calendar (:Calendar or cal)

Looks like that Calendar.vim hooks are always installed and hook methods don't check if any wiki actually exist. Hot and dirty fix for me at the moment:

--- vimwiki/autoload/vimwiki/diary.vim	2017-01-15 15:43:06.837918480 +0100
+++ vimwiki/autoload/vimwiki/diary.vim	2017-01-15 15:42:49.651220557 +0100
@@ -284,6 +284,9 @@
 
 " Sign function.
 function vimwiki#diary#calendar_sign(day, month, year) "{{{
+  if len(g:vimwiki_list) <= 0
+    return
+  endif
   let day = s:prefix_zero(a:day)
   let month = s:prefix_zero(a:month)
   let sfile = VimwikiGet('path').VimwikiGet('diary_rel_path').

[tinmarino]

Closing <= Fixed with your proposition: quick but not so dirty: early returns are actually utlra clean according to me.
Thanks