diff --git a/graphify/build.py b/graphify/build.py
index 1e040420e..5893ef2aa 100644
--- a/graphify/build.py
+++ b/graphify/build.py
@@ -311,8 +311,10 @@ def build(
     return build_from_json(combined, directed=directed, root=root)
 
 
-def _norm_label(label: str) -> str:
+def _norm_label(label: str | None) -> str:
     """Canonical dedup key — Unicode-aware, preserves CJK/word characters."""
+    if not isinstance(label, str):
+        label = "" if label is None else str(label)
     label = unicodedata.normalize("NFKC", label)
     return re.sub(r"[\W_ ]+", " ", label.casefold(), flags=re.UNICODE).strip()
 
diff --git a/graphify/dedup.py b/graphify/dedup.py
index b2885fe5c..913975a26 100644
--- a/graphify/dedup.py
+++ b/graphify/dedup.py
@@ -15,8 +15,10 @@
 
 # ── helpers ───────────────────────────────────────────────────────────────────
 
-def _norm(label: str) -> str:
+def _norm(label: str | None) -> str:
     """Lowercase + collapse non-alphanumeric runs to space (Unicode-aware)."""
+    if not isinstance(label, str):
+        label = "" if label is None else str(label)
     label = unicodedata.normalize("NFKC", label)
     return re.sub(r"[\W_]+", " ", label.casefold(), flags=re.UNICODE).strip()
 
diff --git a/graphify/export.py b/graphify/export.py
index e9f7b5040..26fb20aca 100644
--- a/graphify/export.py
+++ b/graphify/export.py
@@ -102,8 +102,10 @@ def _obsidian_tag(name: str) -> str:
     return re.sub(r"[^a-zA-Z0-9_\-/]", "", name.replace(" ", "_"))
 
 
-def _strip_diacritics(text: str) -> str:
+def _strip_diacritics(text: str | None) -> str:
     import unicodedata
+    if not isinstance(text, str):
+        text = "" if text is None else str(text)
     nfkd = unicodedata.normalize("NFKD", text)
     return "".join(c for c in nfkd if not unicodedata.combining(c))
 
diff --git a/graphify/serve.py b/graphify/serve.py
index a349f511b..6e05b6a98 100644
--- a/graphify/serve.py
+++ b/graphify/serve.py
@@ -51,8 +51,10 @@ def _communities_from_graph(G: nx.Graph) -> dict[int, list[str]]:
     return communities
 
 
-def _strip_diacritics(text: str) -> str:
+def _strip_diacritics(text: str | None) -> str:
     import unicodedata
+    if not isinstance(text, str):
+        text = "" if text is None else str(text)
     nfkd = unicodedata.normalize("NFKD", text)
     return "".join(c for c in nfkd if not unicodedata.combining(c))