fix: handle YAML null values for list config fields

PyYAML parst auskommentierte Listen als None statt []. Da der Key
vorhanden ist, greift .get(key, []) nicht. Drei Fixes:
- extractor.py, differ.py: `or []` statt Default-Argument
- config.py: _deep_update überspringt None-Override auf List-Defaults

Tritt auf bei `ignore_selectors` und `ignore_patterns` in config.yaml.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scanner/config.py

@@ -106,5 +106,7 @@ def _deep_update(base: dict, override: dict) -> None:
     for k, v in override.items():
         if isinstance(v, dict) and isinstance(base.get(k), dict):
             _deep_update(base[k], v)
+        elif v is None and isinstance(base.get(k), list):
+            pass  # YAML null on a list field = "not set" → keep default
         else:
             base[k] = v

scanner/differ.py

@@ -17,7 +17,7 @@ def normalize_text(text: str, cfg: dict) -> str:
     norm_cfg = cfg.get("normalization", {})
     if norm_cfg.get("collapse_whitespace", True):
         text = re.sub(r"\s+", " ", text).strip()
-    for pattern in norm_cfg.get("ignore_patterns", []):
+    for pattern in (norm_cfg.get("ignore_patterns") or []):
         text = re.sub(pattern, "[IGNORED]", text)
     return text
 

scanner/extractor.py

@@ -47,7 +47,7 @@ def extract_page(html: str, url: str, cfg: dict | None = None) -> dict:
     soup = BeautifulSoup(html, "lxml")
 
     # Remove ignored selectors before text extraction
-    ignore_selectors = cfg.get("normalization", {}).get("ignore_selectors", [])
+    ignore_selectors = cfg.get("normalization", {}).get("ignore_selectors") or []
     for sel in ignore_selectors:
         for el in soup.select(sel):
             el.decompose()