fix wrong option on checking empty variable

reinstall-magisk-on-lineageos

@@ -5,7 +5,7 @@ set -e
 PHONE_ADB_SERIAL_NUMBER=${ADB_DEVICE} # The adb serial number can be found by running `adb devices`.
 if [$PHONE_ADB_SERIAL_NUMBER = '']; then
     PHONE_ADB_SERIAL_NUMBER=$(echo $(adb devices) | sed -rn 's/(^|(.* ))([^ ]*) device(( .*)|$)/\3/; T; p; q')
-    if [[ -n $PHONE_ADB_SERIAL_NUMBER ]]; then
+    if [[ -z $PHONE_ADB_SERIAL_NUMBER ]]; then
         print_message "ERROR: no suitable phone connected"
         exit 1
     fi