title: Null pointer exception when using ProGuard
body: <p>I am getting <code>NullPointerException</code> at a line in my code. But when not using ProGuard, everything works just fine.</p>
  
  <p>This is the stack trace:</p>
  
  <pre><code>java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object[] java.util.Collection.toArray()' on a null object reference
                                                                       at java.util.ArrayList.addAll(ArrayList.java:188)
                                                                       at com.random.testing.Details$3.a(Unknown Source)
                                                                       at c.g$a$1$1.run(Unknown Source)
                                                                       at android.os.Handler.handleCallback(Handler.java:739)
                                                                       at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                       at android.os.Looper.loop(Looper.java:148)
                                                                       at android.app.ActivityThread.main(ActivityThread.java:5461)
                                                                       at java.lang.reflect.Method.invoke(Native Method)
                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
  </code></pre>
  
  <p>Here's my <code>proguard-rules.pro</code>:</p>
  
  <pre><code>-dontwarn com.squareup.okhttp.**
  -dontwarn retrofit2.Platform$Java8
  -dontwarn okio.**
  
  -dontnote retrofit2.Platform
  
  -keepattributes Signature
  -keepattributes Exceptions
  
  -keep class android.support.v7.widget.SearchView { *; }
  </code></pre>