diff --git a/manager/app.py b/manager/app.py
index 2d8ae1e..61f31f9 100644
--- a/manager/app.py
+++ b/manager/app.py
@@ -215,12 +215,19 @@ def graph_data():
         level = 1
         anon_ips = []
         for iface in ifaces:
+            addr_json = iface.get("addresses_json")
             try:
-                addrs = json.loads(iface.get("addresses_json", "[]"))
-            except (json.JSONDecodeError, TypeError):
+                if addr_json is None:
+                    addrs = []
+                else:
+                    addrs = json.loads(addr_json)
+                    if not isinstance(addrs, list):
+                        addrs = []
+            except (json.JSONDecodeError, TypeError, AttributeError):
                 addrs = []
+
             for addr in addrs:
-                ip_bare = addr.split("/")[0]
+                ip_bare = addr.split("/")[0] if isinstance(addr, str) else str(addr)
                 if is_public_ip(ip_bare):
                     level = 0
                 anon_ips.append(anonymize_ip(addr))
diff --git a/manager/db.py b/manager/db.py
index 5ca777e..c34bf4f 100644
--- a/manager/db.py
+++ b/manager/db.py
@@ -71,7 +71,7 @@ def init_db():
             agent_id TEXT NOT NULL,
             interface_name TEXT NOT NULL,
             mac_address TEXT,
-            addresses_json TEXT,
+            addresses_json TEXT NOT NULL DEFAULT '[]',
             is_virtual INTEGER NOT NULL DEFAULT 0,
             vpn_type TEXT,
             last_seen_at INTEGER NOT NULL,
@@ -92,6 +92,13 @@ def init_db():
         CREATE INDEX IF NOT EXISTS idx_alarms_agent_status ON alarms(agent_id, status);
     """)
     conn.commit()
+
+    # Migration: backfill any NULL addresses_json from before the NOT NULL default
+    conn.execute("""
+        UPDATE agent_interfaces SET addresses_json = '[]'
+        WHERE addresses_json IS NULL
+    """)
+    conn.commit()
     logger.info("Database initialized at %s", DB_PATH)