Proguard和mixpanel问题

在启用proguard时，我收到以下警告

**警告：com.mixpanel.android.mpmetrics.Tweaks：可以't find referenced class com.mixpanel.android.mpmetrics.Tweaks$TweakType Warning:there were 1 unresolved references to classes or interfaces. You may need to add missing library jars or update their versions. If your code works fine without the missing classes, you can suppress the warnings with ' -dontwarn'选项 . （http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedclass）：app：proguardStageRelease FAILED错误：任务':app:proguardStageRelease'的执行失败 .

java.io.IOException：请先纠正上述警告 . **

logcat on put -dontwarn com.mixpanel . **

java.lang.NullPointerException
        at com.leadsquared.app.LeadsActivity.onCreateOptionsMenu(Unknown Source)
        at android.app.Activity.onCreatePanelMenu(Activity.java:2546)
        at android.support.v4.app.o.onCreatePanelMenu(Unknown Source)
        at android.support.v7.internal.view.k.onCreatePanelMenu(Unknown Source)
        at android.support.v7.app.aj.onCreatePanelMenu(Unknown Source)
        at android.support.v7.internal.view.k.onCreatePanelMenu(Unknown Source)
        at android.support.v7.internal.a.b.g(Unknown Source)
        at android.support.v7.internal.a.c.run(Unknown Source)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5086)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
        at dalvik.system.NativeStart.main(Native Method)

proguard-rules.pro文件是这样的

-dontshrink
 -dontoptimize
 -dontpreverify
   -dontwarn okio.**
      -dontwarn com.mixpanel.**
  -keep class com.squareup.okhttp.** { *; }
    -dontwarn org.xmlpull.v1.**
    -dontwarn com.squareup.**
      -keep interface com.squareup.okhttp.** { *; }
     -keepclasseswithmembers class * {
       void onClick*(...);
      }
      -keepclasseswithmembers class * {
      *** *Callback(...);
         }

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