Cannot map :WhichKey "<BS>"

[aldevv]

Environment (please complete the following information):

OS: Linux
(Neo)Vim version: 0.5
Have you reproduced with a minimal vimrc: yes

Describe the bug
:WhichKey "" works when typing it by hand, but mapping it to a key produces message:

E114: Missing quote ")
E116: Invalid arguments for function which_key#start

To Reproduce
Steps to reproduce the behavior:

Make some mappings with as leader (optional)
:nnoremap :WhichKey "<BS>"<CR>
Error shows

Expected behavior
Whichkey should function as it normally does in command mode

[BrotifyPacha]

You dont have to place your exact key code in the WhichKey argument, you can use anything you want as long as it corresponds to your registered "Key" in which_key#register.
So the following code opens up g:my_backspace_dict upon pressing :

:nnoremap <BS> :WhichKey "oof"<CR>
let g:my_backspace_dict = {
      \ 'j' : ['j', 'my mapping'],
      \ }
call which_key#register('oof', "g:my_backspace_dict")

[aldevv]

While this does what i wanted

:nnoremap <BS> :WhichKey "oof"<CR>

I prefer this other way you mentioned, which also works.

:nnoremap <BS> :WhichKey "\<BS\>"<CR>

hope this helps anyone.

[liuchengxu]

@BrotifyPacha made a very good point here. I have added this kind of question into FAQ in README so that others can find this easier.