diff --git a/app/src/main/java/com/example/lzwcai_terminal_temi/SettingsActivity.kt b/app/src/main/java/com/example/lzwcai_terminal_temi/SettingsActivity.kt
index bc87602..8caaa4a 100644
--- a/app/src/main/java/com/example/lzwcai_terminal_temi/SettingsActivity.kt
+++ b/app/src/main/java/com/example/lzwcai_terminal_temi/SettingsActivity.kt
@@ -402,8 +402,8 @@ class SettingsActivity : AppCompatActivity() {
         if (saved.isNotEmpty()) {
             return saved
         }
-        val serial = runCatching { robot.serialNumber }.getOrDefault("").trim()
-        val deviceId = if (serial.isNotEmpty()) serial else "unknown-device"
+        val serial = runCatching { robot.serialNumber }.getOrDefault("")?.trim()
+        val deviceId = if (serial?.isNotEmpty() == true) serial else "unknown-device"
         prefs.edit().putString(HttpManager.PREF_KEY_DEVICE_ID, deviceId).apply()
         return deviceId
     }