fix: Handle None values from empty YAML fields to prevent AttributeError (fixes #212)

[thorstenhornung1]

My AI skills exceed my Python skills. Therefore, I have used Claude code and my debug skills to address this issue.

Problem

The integration crashes with AttributeError: 'NoneType' object has no attribute 'lower' when scenes.yaml contains empty YAML fields. This occurs because the YAML parser (yaml.FullLoader) interprets empty fields as None values, which are then passed to functions expecting string values.

Example problematic YAML:

- id: living_room_bright
  name: Living Room Bright
  entities:
    light.living_room:
      state: "on"
      brightness: 255
      color_mode:           # Empty field parsed as None
      rgb_color:            # Empty field parsed as None

Error trace:

AttributeError: 'NoneType' object has no attribute 'lower'
  at helpers.py in get_area_from_entity_id()
  when attempting None.lower() on entity_id parameter

Root Cause

When YAML fields are left empty (e.g., brightness:, color_mode:), the yaml.FullLoader parser returns None for these values. The integration previously had no protection against these unintentional None values, causing crashes when:

1. Empty attribute fields in scene configurations were copied directly to entity attributes
2. Helper functions received None instead of expected string values for entity IDs
3. UI fallback logic didn't account for None returns from helper functions

This is distinct from the intentional use of None for "don't care" semantics in state values, which must be preserved for proper scene matching logic.

Solution

Implemented a two-layer defense-in-depth strategy:

1. Prevention Layer (Primary Defense)

Filter out None values at the source when reading scene attributes from YAML, preventing unintentional None values from entering the system.

2. Defensive Layer (Robustness)

Add explicit None handling throughout the codebase to gracefully handle edge cases and improve overall robustness.

This approach ensures:

• Unintentional None values from empty YAML fields are filtered out
• Intentional None state values for "don't care" semantics are preserved
• The system remains robust even if None values slip through validation
• User-facing UI always displays meaningful fallback values

Changes Made

1. Prevention Layer

File: /custom_components/stateful_scenes/StatefulScenes.py
Location: Lines 734-737

Added None value filtering when copying scene attributes from YAML:

if domain in ATTRIBUTES_TO_CHECK:
    for attribute, value in scene_attributes.items():
        if attribute in ATTRIBUTES_TO_CHECK.get(domain):
            # Filter out None values from empty YAML fields
            # Note: None state values are preserved for "don't care" semantics
            if value is not None:
                attributes[attribute] = value

Impact: Prevents empty YAML fields from being copied as None attributes to entity configurations

---

2. Defensive Layer

File: /custom_components/stateful_scenes/helpers.py

Added None handling to 4 helper functions with updated type hints:

• get_id_from_entity_id() - Lines 10-15
• get_name_from_entity_id() - Lines 18-22
• get_icon_from_entity_id() - Lines 25-29
• get_area_from_entity_id() - Lines 32-45

All functions now accept str | None and return str | None, with early None checks.

File: /custom_components/stateful_scenes/StatefulScenes.py
Location: Lines 35-42

Added None check to area_name() function

File: /custom_components/stateful_scenes/config_flow.py

Added fallback values for UI display when helper functions return None:

• Lines 163-166: Scene name and area with fallbacks
• Line 250: Scene name with fallback "Unknown Scene"
• Line 302: Entity name with fallback "Unknown Entity"

Semantic Preservation

This fix carefully preserves the existing behavior where None state values are used intentionally to mean "don't care" during scene matching:

• Before: Scene with state: None for an entity matches regardless of current state
• After: Same behavior preserved - only filters None from attributes, not from state fields

Testing

Tested scenarios:

1. Empty YAML fields - no crashes, attributes not copied
2. None state values - "don't care" matching still works
3. Helper function robustness - graceful None returns
4. UI fallback values - proper display of fallback text
5. Regression testing - existing functionality unchanged

Breaking Changes

None. This is a pure bug fix with no breaking changes:

• Existing scenes continue to work unchanged
• Intentional None semantics are preserved
• Only prevents crashes from unintentional empty YAML fields
• All APIs maintain backward compatibility

🤖 Generated with Claude Code

[hugobloem]

Many thanks!