在magit-status buffer下checkout PR的时候发现auth错误。复现如下：可能需要删除之前存过的auth，分别在_~/.emacs.d/.local/etc/autoinfo.gpg_ 和_~/.authinfo.gpg_里， M-x magit-status -> b -> y, 然后输入用户名密码。
magit版本为magit-20181015.1832
得到如下错误。
Debugger entered--Lisp error: (wrong-type-argument stringp nil)
encode-coding-string(nil utf-8)
ghub--auth("api.github.com" magit "ztlevi" nil)
#f(compiled-function () #<bytecode 0x43f45e0d>)()
ghub--retrieve(nil #s(ghub--req :url #s(url :type "https" :user nil :password nil :host "api.github.com" :portspec nil :filename "/repos/hlissner/.emacs.d/pulls" :target nil :attributes nil :fullness t :silent nil :use-cookies t :asynchronous t) :forge nil :silent nil :method "GET" :headers #f(compiled-function () #<bytecode 0x43f45e0d>) :handler ghub--handle-response :unpaginate nil :noerror nil :reader nil :callback nil :errorback nil :value nil :extra nil))
ghub-request("GET" "/repos/hlissner/.emacs.d/pulls" nil :query nil :payload nil :headers nil :silent nil :unpaginate nil :noerror nil :reader nil :username nil :auth magit :host nil :callback nil :errorback nil :extra nil)
ghub-get("/repos/hlissner/.emacs.d/pulls" nil :auth magit)
magit-read-pull-request("Checkout pull request")
byte-code("\300\301!C\207" [magit-read-pull-request "Checkout pull request"] 2)
call-interactively(magit-checkout-pull-request)
magit-invoke-popup-action(121)
funcall-interactively(magit-invoke-popup-action 121)
call-interactively(magit-invoke-popup-action nil nil)
command-execute(magit-invoke-popup-action)