fix: address review feedback on saving session entity fallback

- Distinguish "attribute genuinely missing" from "attribute present but
  an empty list" using a sentinel, so the binary_sensor -> event fallback
  no longer misfires when the configured entity is valid but currently
  has no events (a normal, common state).
- Isolate the new regression test's mutation of my_predbat.args behind a
  save/restore, matching the pattern used by other tests in this suite.

Addresses Copilot review comments on PR #4585.

Author: springfall2008

apps/predbat/octopus.py

@@ -35,6 +35,10 @@
 DATE_STR_FORMAT = "%Y-%m-%d"
 DATE_TIME_STR_FORMAT = "%Y-%m-%dT%H:%M:%S%z"
 
+# Sentinel distinguishing "attribute not present on the entity" from a genuinely empty list,
+# since both would otherwise look the same (falsy) to callers.
+_ATTRIBUTE_UNSET = object()
+
 # Night-rate window definitions: start time, end time, whether the window crosses midnight.
 # Keys: "eco7" (Economy 7), "go" (Octopus GO / generic day-night), "iog" (Intelligent GO TOU).
 OCTOPUS_NIGHT_RATE_WINDOWS = {
@@ -2939,18 +2943,22 @@ def fetch_octopus_sessions(self, axle_sessions=None):
             entity_id = self.get_arg("octopus_saving_session", indirect=False)
             if entity_id:
                 state = self.get_arg("octopus_saving_session", False)
-                joined_events = self.get_state_wrapper(entity_id=entity_id, attribute="joined_events")
-                available_events = self.get_state_wrapper(entity_id=entity_id, attribute="available_events")
-                if not joined_events and not available_events:
-                    # Legacy binary_sensor entities carry neither attribute - fall back to the
-                    # newer event entity naming convention, but only adopt it if it actually has data
+                joined_events = self.get_state_wrapper(entity_id=entity_id, attribute="joined_events", default=_ATTRIBUTE_UNSET)
+                available_events = self.get_state_wrapper(entity_id=entity_id, attribute="available_events", default=_ATTRIBUTE_UNSET)
+                if joined_events is _ATTRIBUTE_UNSET and available_events is _ATTRIBUTE_UNSET:
+                    # Legacy binary_sensor entities carry neither attribute at all - fall back to the
+                    # newer event entity naming convention, but only adopt it if it actually has data.
+                    # A configured entity that has the attributes but with no events right now (empty
+                    # lists) is a valid state and must not trigger this fallback.
                     fallback_entity_id = entity_id.replace("binary_sensor.", "event.").replace("_sessions", "_session_events")
-                    fallback_joined_events = self.get_state_wrapper(entity_id=fallback_entity_id, attribute="joined_events")
-                    fallback_available_events = self.get_state_wrapper(entity_id=fallback_entity_id, attribute="available_events")
-                    if fallback_joined_events or fallback_available_events:
+                    fallback_joined_events = self.get_state_wrapper(entity_id=fallback_entity_id, attribute="joined_events", default=_ATTRIBUTE_UNSET)
+                    fallback_available_events = self.get_state_wrapper(entity_id=fallback_entity_id, attribute="available_events", default=_ATTRIBUTE_UNSET)
+                    if fallback_joined_events is not _ATTRIBUTE_UNSET or fallback_available_events is not _ATTRIBUTE_UNSET:
                         entity_id = fallback_entity_id
                         joined_events = fallback_joined_events
                         available_events = fallback_available_events
+                joined_events = [] if joined_events is _ATTRIBUTE_UNSET else joined_events
+                available_events = [] if available_events is _ATTRIBUTE_UNSET else available_events
 
             if available_events and not self.get_arg("octopus_saving_auto_join", True):
                 self.log("Octopus: Saving session auto-join is disabled, not joining available events")

apps/predbat/tests/test_saving_session.py

@@ -624,40 +624,43 @@ def test_saving_session_custom_entity_no_rewrite_match(my_predbat):
 friendly_name: Predbat Octopus Power Down For Predbat
 """
 
-    ha.dummy_items.clear()
-    ha.dummy_items["binary_sensor.predbat_octopus_power_down_for_predbat"] = yaml.safe_load(session_binary)
-    ha.dummy_items["sensor.octopus_free_session"] = {}
-    my_predbat.args["octopus_saving_session"] = "binary_sensor.predbat_octopus_power_down_for_predbat"
-    my_predbat.args["octopus_free_session"] = "sensor.octopus_free_session"
-    if "octopus_free_url" in my_predbat.args:
-        del my_predbat.args["octopus_free_url"]
-    if "octopus_saving_session_join" in my_predbat.args:
-        del my_predbat.args["octopus_saving_session_join"]
-    my_predbat.args["octopus_saving_session_octopoints_per_penny"] = 10
-    # Reset throttle so a join is attempted
-    my_predbat.octopus_last_joined_try = None
-
-    ha.service_store_enable = True
-    ha.service_store = []
-    my_predbat.fetch_octopus_sessions()
-    service_result = ha.get_service_store()
-    ha.service_store_enable = False
+    saved_args = my_predbat.args.copy()
+    try:
+        ha.dummy_items.clear()
+        ha.dummy_items["binary_sensor.predbat_octopus_power_down_for_predbat"] = yaml.safe_load(session_binary)
+        ha.dummy_items["sensor.octopus_free_session"] = {}
+        my_predbat.args["octopus_saving_session"] = "binary_sensor.predbat_octopus_power_down_for_predbat"
+        my_predbat.args["octopus_free_session"] = "sensor.octopus_free_session"
+        if "octopus_free_url" in my_predbat.args:
+            del my_predbat.args["octopus_free_url"]
+        if "octopus_saving_session_join" in my_predbat.args:
+            del my_predbat.args["octopus_saving_session_join"]
+        my_predbat.args["octopus_saving_session_octopoints_per_penny"] = 10
+        # Reset throttle so a join is attempted
+        my_predbat.octopus_last_joined_try = None
 
-    join_calls = [svc for svc in service_result if "join" in svc[0]]
-    if len(join_calls) != 1:
-        print(f"ERROR: Expected 1 join call reading available_events from the configured entity, got {len(join_calls)}: {service_result}")
-        failed = True
-    elif join_calls[0][1].get("entity_id") != "binary_sensor.predbat_octopus_power_down_for_predbat":
-        print(f"ERROR: Expected join call to use the configured entity, got {join_calls[0][1]}")
-        failed = True
-    else:
-        print("  PASS: available_events read from the configured entity despite no rewrite match")
+        ha.service_store_enable = True
+        ha.service_store = []
+        my_predbat.fetch_octopus_sessions()
+        service_result = ha.get_service_store()
+        ha.service_store_enable = False
 
-    if not failed:
-        print("PASS: Custom entity name (no rewrite match) auto-join test passed")
+        join_calls = [svc for svc in service_result if "join" in svc[0]]
+        if len(join_calls) != 1:
+            print(f"ERROR: Expected 1 join call reading available_events from the configured entity, got {len(join_calls)}: {service_result}")
+            failed = True
+        elif join_calls[0][1].get("entity_id") != "binary_sensor.predbat_octopus_power_down_for_predbat":
+            print(f"ERROR: Expected join call to use the configured entity, got {join_calls[0][1]}")
+            failed = True
+        else:
+            print("  PASS: available_events read from the configured entity despite no rewrite match")
 
-    # Restore default throttle state so we do not leak it to other tests
-    my_predbat.octopus_last_joined_try = None
+        if not failed:
+            print("PASS: Custom entity name (no rewrite match) auto-join test passed")
+    finally:
+        my_predbat.args = saved_args
+        # Restore default throttle state so we do not leak it to other tests
+        my_predbat.octopus_last_joined_try = None
 
     return failed