Fix some custom types

* lisp/mpc.el (mpc-cover-image-re):
* lisp/org/oc-csl.el (org-cite-csl-locales-dir)
(org-cite-csl-styles-dir):
* lisp/org/org-plot.el (org-plot/preset-plot-types): Fix :type.

lisp/mpc.el

@@ -964,7 +964,7 @@ If PLAYLIST is t or nil or missing, use the main playlist."
 
 (defcustom mpc-cover-image-re nil ; (rx (or ".jpg" ".jpeg" ".png") string-end)
   "If non-nil, it is a regexp that should match a valid cover image."
-  :type '(regexp)
+  :type '(choice (const nil) regexp)
   :version "28.1")
 
 (defun mpc-secs-to-time (secs)

lisp/org/oc-csl.el

@@ -123,7 +123,7 @@ If nil then only the fallback en-US locale will be available."
   :group 'org-cite
   :package-version '(Org . "9.5")
   :type '(choice
-          (dir :tag "Locales directory")
+          (directory :tag "Locales directory")
           (const :tag "Use en-US locale only" nil))
   :safe t)
 
@@ -134,7 +134,7 @@ directory.  This variable is ignored when style file is absolute."
   :group 'org-cite
   :package-version '(Org . "9.5")
   :type '(choice
-          (dir :tag "Styles directory")
+          (directory :tag "Styles directory")
           (const :tag "Use absolute file names" nil))
   :safe t)
 

lisp/org/org-plot.el

@@ -392,7 +392,7 @@ be set.
    Accepts string, nil, or lambda function which returns string
    or nil.  Defaults to nil."
   :group 'org-plot
-  :type '(alist :value-type (symbol group)))
+  :type 'alist)
 
 (defvar org--plot/radar-template
   "### spider plot/chart with gnuplot