To figure out the problem, create a group without giving a group label.
The value of the field "grouplabel" which is to be persisted is an empty string.
In Oracle, empty string are persisted to null (fair enough). The problem is that when we fetch the persisted data, the value of the field "grouplabel" is not an empty string anymore but null.
This is not really consistent with other db behaviours (such as h2, postgres) and could lead to some troubles.
Note that here we use org.nuxeo.ecm.directory.sql.SQLSession. This behavior is not observed with org.nuxeo.ecm.core.storage.sql.coremodel.SQLSession with oracle.