{"id":"null-root-returns-empty-list","text":"All tree traversal solutions return `[]` (not `None` or an error) when given a null/None root, enforced by early guard clauses or loop conditions that short-circuit naturally.","truth_value":"IN","source":"entries/2026/06/06/binary-tree-preorder-traversal-solution.md","source_url":"","source_hash":"","justifications":[],"dependents":[],"metadata":{},"created_at":"","updated_at":"","reviewed_at":"","verified_at":"","retracted_at":"","explanation":{"steps":[{"node":"null-root-returns-empty-list","truth_value":"IN","reason":"premise"}]}}