Tweak incorrect case in --cygwin-extra-packages

Author: dra27

master_changes.md

@@ -21,7 +21,7 @@ users)
 ## Plugins
 
 ## Init
-  * ◈ New option `opam init --cygwin-extra-packages=CYGWIN_PKGS --cygwin-internal-install`, to specify additional packages for internal Cygwin [#5930 @moyodiallo - fix #5834]
+  * ◈ New option `opam init --cygwin-extra-packages=CYGWIN_PKGS --cygwin-internal-install`, to specify additional packages for internal Cygwin [#5930, #5964 @moyodiallo - fix #5834]
 
 ## Config report
 

src/client/opamCommands.ml

@@ -435,6 +435,8 @@ let init cli =
         bad_arg "no-cygwin-setup" "cygwin-extra-packages"
       | `none, Some _, Some _ ->
         bad_arg "cygwin-location" "cygwin-extra-packages"
+      | `none, None, None ->
+        None
       | (`internal | `none), None, pkgs ->
         Some (`internal
                 (OpamStd.Option.default [] pkgs