android- XML OnClick方法不工作

，我发现了以下错误：android- XML OnClick方法不工作

04-16 14:29:02.281 4845-4845/com.example.rswat.mychatapp E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.example.rswat.mychatapp, PID: 4845 
java.lang.IllegalStateException: Could not execute method for android:onClick 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293) 
    at android.view.View.performClick(View.java:5637) 
    at android.view.View$PerformClick.run(View.java:22429) 
    at android.os.Handler.handleCallback(Handler.java:751) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6119) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 
    Caused by: java.lang.reflect.InvocationTargetException 
    at java.lang.reflect.Method.invoke(Native Method) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
    at android.view.View.performClick(View.java:5637)  
    at android.view.View$PerformClick.run(View.java:22429)  
    at android.os.Handler.handleCallback(Handler.java:751)  
    at android.os.Handler.dispatchMessage(Handler.java:95)  
    at android.os.Looper.loop(Looper.java:154)  
    at android.app.ActivityThread.main(ActivityThread.java:6119)  
    at java.lang.reflect.Method.invoke(Native Method)  
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)  
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)  
    Caused by: java.lang.IllegalArgumentException: Invalid to: 
    at com.google.firebase.messaging.RemoteMessage$Builder.<init>(Unknown Source) 
    at com.example.rswat.mychatapp.MainActivity.onClick(MainActivity.java:33) 
    at java.lang.reflect.Method.invoke(Native Method)  
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)  
    at android.view.View.performClick(View.java:5637)  
    at android.view.View$PerformClick.run(View.java:22429)  
    at android.os.Handler.handleCallback(Handler.java:751)  
    at android.os.Handler.dispatchMessage(Handler.java:95)  
    at android.os.Looper.loop(Looper.java:154)  
    at android.app.ActivityThread.main(ActivityThread.java:6119)  
    at java.lang.reflect.Method.invoke(Native Method)  
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)  
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

请帮助...！非常感谢...！

code