const Goa = imports.gi.Goa;

let client = Goa.Client.new_sync(null);
let accounts = client.get_accounts();
for (let i in accounts) {
    //Now account is a instance of org.gnome.OnlineAccounts.Account
    //DBus interface (GoaAccountProxy instance)
    let account = accounts[i].get_account();

    //This prints null (the interface has no signals)
    print(account.get_interface_info().signals);
}

let info = Gio.DBusInterfaceInfo.new_for_xml (<org.gnome.OnlineAccounts.Account as XML>);
//This doesn't prints null, but nothing (so, an empty array)
//Why is that difference?
print(info.signals);