Empty name for group name

[follow39]

Hi there,
I'm trying to use caskey and notice some weird behaviour, it cannot set group name for whichkey when initialization with function is used. Is it suppose to be or I use the plugin wrong?
Config:

["<leader>t"] = function()
    local builtin = require('telescope.builtin')

    return {
        name = "telescope",
        mode = {'n', 'v'},

        t = {act = builtin.treesitter, desc = 'treesitter'},
        s = {act = builtin.symbols, desc = 'symbols'},
        f = {act = builtin.git_files, desc = 'git files'},
        a = {act = builtin.find_files, desc = 'find files'},
        o = {act = builtin.oldfiles, desc = 'old files'},
        l = {act = builtin.live_grep, desc = 'live grep'},
        s = {act = builtin.grep_string, desc = 'grep string'},
        c = {act = builtin.commands, desc = 'commands'},
        k = {act = builtin.keymaps, desc = 'keymaps'},
        b = { act = 
        function() 
            builtin.buffers({
                sort_mru=true, 
                ignore_current_buffer=true
            })
        end,
        desc = 'buffers'},
    }
end

Image: