JS ERROR: Error: Tried to construct an object without a GType; are you using GObject.registerClass() when inheriting from a GObject type?
CustomDialog@/home/shuhao/.local/share/gnome-shell/extensions/MultiClock@mibus.org/extension.js:163:9
_init/<@/home/shuhao/.local/share/gnome-shell/extensions/MultiClock@mibus.org/extension.js:77:15
addAction/<@resource:///org/gnome/shell/ui/popupMenu.js:538:13
activate@resource:///org/gnome/shell/ui/popupMenu.js:191:14
vfunc_button_release_event@resource:///org/gnome/shell/ui/popupMenu.js:138:14
FWIW this was broken by GNOME 3.36, the new version in git fixes it and I've uploaded to extensions.gnome.org (which will take a while to review before becoming available). Thanks for reporting!
When I click Other..., I get the following error: