Strip null values from optional Login cipher fields

Some Login ciphers stored in Vaultwarden have explicit `null` values for optional fields (e.g. `totp`, `passwordRevisionDate`, `username`, `uris`) rather than the field being absent. Upstream Bitwarden's server serializes these with `skip_serializing_if = "Option::is_none"` so the fields are always absent when unset, never `null`.

The 2026.5+ Bitwarden clients (using the new sdk-internal WASM SDK) route JS `null` values into `EncString::deserialize` instead of short-circuiting `Option<T>` to `None`, and panic with `invalid type: unit value, expected a valid string`. Serde aborts on the first failure, so one bad cipher causes the entire vault to fail to load.

Match upstream's shape by stripping explicit `null` values from the affected keys before emit. The legacy `uri` field (set unconditionally to `Value::Null` at line 261 for old mobile client compat) is deliberately not stripped.

Refs: #7361, bitwarden/clients#21135

src/db/models/cipher.rs

@@ -280,6 +280,23 @@ impl Cipher {
             if let Some(pw_revision) = type_data_json["passwordRevisionDate"].as_str() {
                 type_data_json["passwordRevisionDate"] = json!(validate_and_format_date(pw_revision));
             }
+
+            // Strip `null`s from optional Login fields — newer WASM clients panic (see #7361).
+            if let Value::Object(ref mut map) = type_data_json {
+                for key in [
+                    "password",
+                    "username",
+                    "totp",
+                    "autofillOnPageLoad",
+                    "fido2Credentials",
+                    "passwordRevisionDate",
+                    "uris",
+                ] {
+                    if map.get(key).is_some_and(Value::is_null) {
+                        map.remove(key);
+                    }
+                }
+            }
         }
 
         // Fix secure note issues when data is invalid