Behavior of echo :

[mattn]

trafficstars

:echo :

Vim throw two errors for this statement.

E121: Undefined variable: :
E15: Invalid expression: :

https://github.com/vim-jp/vim-vimlparser/blob/b5f83738ba1baf012b9910487e5e38d577a916a5/autoload/vimlparser.vim#L3391

If modify this part to 1, error E121 is returned. We should design behavior what error should be returned.