How to address the appointment table ?

I wrote an add-on plugin for A+ which generates invoices.

The add-on made use of $appointments->app_table to get the name of the appointment table in the DB and construct a SQL query.

Everything worked well till last update of A+.

Now $appointments->app_table returns an empty string and the query doesn’t work any more.

Can you help me in solving the problems ?

Can I still use $appointments->app_table ?

Thanks for yor help

Kind regards