According to documentation [1] a menu item has a target attribute, which is "the parameter to pass when activating the action". Furthermore, the action "Activate" method specifies "If the action activation requires a parameter then this parameter must be given in the second parameter (av).".
Also implements a TODO in the code.
[1] https://wiki.gnome.org/Projects/GLib/GApplication/DBusAPI
CCBUG: 418385