fix unit fixed setting postgresql version into app_peer_data

Author: BalabaDmitri

src/charm.py

@@ -1585,7 +1585,9 @@ def _validate_database_version(self):
         peer_db_version = self.app_peer_data.get("database-version")
 
         if self.unit.is_leader() and peer_db_version is None:
-            self.app_peer_data.update({"database-version": self._patroni.get_postgresql_version()})
+            _psql_version = self._patroni.get_postgresql_version()
+            if _psql_version is not None:
+                self.app_peer_data.update({"database-version": _psql_version})
             return
 
         if peer_db_version != self._patroni.get_postgresql_version():

tests/unit/test_charm.py

@@ -1372,7 +1372,7 @@ def test_on_peer_relation_changed(
             self.harness.update_relation_data(
                 self.rel_id,
                 self.charm.app.name,
-                {"cluster_initialised": "True", "members_ips": '["1.1.1.1"]'},
+                {"cluster_initialised": "True", "members_ips": '["1.1.1.1"]', "database_version": "14"},
             )
             self.harness.set_leader()
         _reconfigure_cluster.return_value = False