Mapping does not contain any object classes

What causes this issue?

You must record the object classes in the "Object Classes" table for
which an entry in the directory is to be synchronized with the
SAP system.
If the system creates a new entry in the directory, the new entry is
assigned this object class.
If the system searches for an entry in the directory, only entries
which have all object classes entered here are found.
Although it is possible to enter an asterisk ("*") as the object class,
we recommend that you do not do so, since this will lead to errors
when creating new entries.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.