eval/encode: Make sure that encoder can encode NULL variables

Adds two undocumented v: variables: _null_list and _null_dict because I do not 
know a reproducible way to get such lists (though I think I heard about this) 
and dictionaries (do not remember hearing about them). NULL strings are obtained 
using $XXX_UNEXISTENT_VAR_XXX.

Fixes crash in json_encode($XXX_UNEXISTENT_VAR_XXX). Other added tests worked 
fine before this commit.

1 files changed, 14 insertions, 0 deletions

diff --git a/test/functional/eval/msgpack_functions_spec.lua b/test/functional/eval/msgpack_functions_spec.lua
index a602bad86f..9e501353a5 100644
--- a/test/functional/eval/msgpack_functions_spec.lua
+++ b/test/functional/eval/msgpack_functions_spec.lua
@@ -686,4 +686,18 @@ describe('msgpackdump() function', function()
         exc_exec('call msgpackdump(' .. val .. ')'))
     end
   end)
+
+  it('can dump NULL string', function()
+    eq({'\196\n'}, eval('msgpackdump([$XXX_UNEXISTENT_VAR_XXX])'))
+    eq({'\196\n'}, eval('msgpackdump([{"_TYPE": v:msgpack_types.binary, "_VAL": [$XXX_UNEXISTENT_VAR_XXX]}])'))
+    eq({'\160'}, eval('msgpackdump([{"_TYPE": v:msgpack_types.string, "_VAL": [$XXX_UNEXISTENT_VAR_XXX]}])'))
+  end)
+
+  it('can dump NULL list', function()
+    eq({'\144'}, eval('msgpackdump([v:_null_list])'))
+  end)
+
+  it('can dump NULL dictionary', function()
+    eq({'\128'}, eval('msgpackdump([v:_null_dict])'))
+  end)
 end)