java.lang.IllegalMonitorStateException: object not locked by thread before notify()

/*Device Info*/
[硬]设备制造商=Genymotion
[硬]设备型号=Custom
[硬]CPU型号=null
[硬]RAM=1.04 GB
[硬]ROM=13.38 GB
[OS][三方定制系统版本]=Android/vbox86p/vbox86p:8.0.0/OPR6.170623.017/32:userdebug/test-keys
[OS]产品名称(adb shell)=vbox86p
[OS][系统名称]=Android
[OS][Android版本]=8.0.0(26)
[app]versionName=1.0
[app]versionCode=1
/*Exception*/
java.lang.IllegalMonitorStateException: object not locked by thread before notify()
    at java.lang.Object.notify(Native Method)
    at io.github.TomGarden.tetris.Fragments.SettingGameStylePreferenceFragment.lpBGChange(SettingGameStylePreferenceFragment.java:476)
    at io.github.TomGarden.tetris.Fragments.SettingGameStylePreferenceFragment.access$800(SettingGameStylePreferenceFragment.java:57)
    at io.github.TomGarden.tetris.Fragments.SettingGameStylePreferenceFragment$2.onPreferenceChange(SettingGameStylePreferenceFragment.java:231)
    at android.preference.Preference.callChangeListener(Preference.java:1079)
    at android.preference.ListPreference.onDialogClosed(ListPreference.java:282)
    at android.preference.DialogPreference.onDismiss(DialogPreference.java:395)
    at android.app.Dialog$ListenersHandler.handleMessage(Dialog.java:1361)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6541)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

TomGarden / Tetris

java.lang.IllegalMonitorStateException: object not locked by thread before notify() #37