Handle the situation when no data in relation yet (#71)

lib/charms/smtp_integrator/v0/smtp.py

@@ -68,7 +68,7 @@ def _on_config_changed(self, _) -> None:
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 11
+LIBPATCH = 12
 
 PYDEPS = ["pydantic>=2"]
 
@@ -280,7 +280,7 @@ def get_relation_data(self) -> Optional[SmtpRelationData]:
         relation = self.model.get_relation(self.relation_name)
         return self._get_relation_data_from_relation(relation) if relation else None
 
-    def _get_relation_data_from_relation(self, relation: ops.Relation) -> SmtpRelationData:
+    def _get_relation_data_from_relation(self, relation: ops.Relation) -> SmtpRelationData | None:
         """Retrieve the relation data.
 
         Args:
@@ -291,6 +291,8 @@ def _get_relation_data_from_relation(self, relation: ops.Relation) -> SmtpRelati
         """
         assert relation.app
         relation_data = relation.data[relation.app]
+        if not relation_data:
+            return None
         return SmtpRelationData(
             host=typing.cast(str, relation_data.get("host")),
             port=typing.cast(int, relation_data.get("port")),

tests/unit/test_library_smtp.py

@@ -278,3 +278,16 @@ def test_requirer_charm_with_invalid_relation_data_doesnt_emit_event(is_leader):
     harness.add_relation("smtp-legacy", "smtp-provider", app_data=relation_data)
 
     assert len(harness.charm.events) == 0
+
+
+def test_requirer_charm_get_relation_data_without_relation_data():
+    """
+    arrange: set up a charm with smtp relation without any relation data.
+    act: call get_relation_data function.
+    assert: get_relation_data should return None.
+    """
+    harness = Harness(SmtpRequirerCharm, meta=REQUIRER_METADATA)
+    harness.begin()
+    harness.set_leader(True)
+    harness.add_relation("smtp", "smtp-provider", app_data={})
+    assert harness.charm.smtp.get_relation_data() is None