Return empty collections (lists, dicts, sets) instead of None when representing empty states. This reduces null checking boilerplate, prevents null reference errors, and makes code more predictable. When a function returns a collection type, an empty collection communicates "no items" more clearly than None and allows direct operations without defensive checks. Example: ```python # Not recommended def extract_tags(span): if not span.tags: return None # Forces callers to check for None return [tag for tag in span.tags] # Recommended def extract_tags(span): if not span.tags: return [] # Callers can immediately iterate/operate on result return [tag for tag in span.tags] # Usage is simpler and safer tags = extract_tags(span) for tag in tags: # Works directly, no None check needed process_tag(tag) ``` This pattern: - Eliminates common None-check boilerplate - Prevents NullPointerException scenarios - Makes interfaces more predictable - Allows direct operations on return values - Maintains semantic clarity between "no items" vs "invalid/error state" For error conditions or invalid states, raise exceptions or use Optional types instead of returning None.