InMemoryDB: provide None for dbname

gramps/gen/db/generic.py

@@ -2025,13 +2025,14 @@ class DbGeneric(DbWriteBase, DbReadBase, UpdateCallback, Callback):
         """
         In DbGeneric, the database is in a text file at the path
         """
+        name = None
+        if self._directory:
             filepath = os.path.join(self._directory, "name.txt")
             try:
                 with open(filepath, "r") as name_file:
                     name = name_file.readline().strip()
             except (OSError, IOError) as msg:
                 LOG.error(str(msg))
-            name = None
         return name
 
     def _order_by_person_key(self, person):