can't set mapleader in site-specific setting

[rudevdr]

As title said, setting mapleader in site-specific settings doesn't work.

My cvimrc looks like this :

let mapleader = "<C-/>"
site '*://*.reddit.com/*' {
   let mapleader = ","
   unmap j
   map <leader>j scrollDown
}

<C-/> works as mapleader on *.reddit.com but not ,.