title: NPE when calling MockitoAnnotations.initMocks() in AndroidTestCase
body: <p>Trying to use mockito in my AndroidTestCase. I added the dependencies to the build.gradle:</p>
  
  <pre><code>final DEXMAKER_VERSION = '1.2'
  
  dependencies {
      // ...
      androidTestCompile "com.google.dexmaker:dexmaker:${DEXMAKER_VERSION}"
      androidTestCompile "com.google.dexmaker:dexmaker-mockito:${DEXMAKER_VERSION}"
      androidTestCompile 'org.mockito:mockito-core:1.10.19'
  
  }
  </code></pre>
  
  <p>The TestCase with  the mockito initialization:</p>
  
  <pre><code>public class UsersListPresenterTest extends AndroidTestCase {
  
      public void setUp() throws Exception {
          MockitoAnnotations.initMocks(this);
      }
  
      public void testInitialize() throws Exception {
  
      }
  }
  </code></pre>
  
  <p>But as soon as I add any attribute to the class, even before adding any annotation the test start to crash:</p>
  
  <pre><code>public class UsersListPresenterTest extends AndroidTestCase {
  
      String mockString;
  
      public void setUp() throws Exception {
          MockitoAnnotations.initMocks(this);
      }
  
      public void testInitialize() throws Exception {
  
      }
  }
  </code></pre>
  
  <p>With the following stacktrace</p>
  
  <pre><code>java.lang.NullPointerException: Attempt to invoke virtual method 
      'java.lang.Class java.lang.Object.getClass()' on a null object reference
  at com.google.dexmaker.mockito.DexmakerMockMaker.getInvocationHandlerAdapter(DexmakerMockMaker.java:80)
  at com.google.dexmaker.mockito.DexmakerMockMaker.getHandler(DexmakerMockMaker.java:75)
  at org.mockito.internal.util.MockUtil.isMockitoMock(MockUtil.java:74)
  at org.mockito.internal.util.MockUtil.isMock(MockUtil.java:66)
  at org.mockito.internal.configuration.injection.scanner.MockScanner.isMockOrSpy(MockScanner.java:86)
  at org.mockito.internal.configuration.injection.scanner.MockScanner.preparedMock(MockScanner.java:72)
  at org.mockito.internal.configuration.injection.scanner.MockScanner.scan(MockScanner.java:61)
  at org.mockito.internal.configuration.injection.scanner.MockScanner.addPreparedMocks(MockScanner.java:47)
  at org.mockito.internal.configuration.InjectingAnnotationEngine.injectMocks(InjectingAnnotationEngine.java:96)
  at org.mockito.internal.configuration.InjectingAnnotationEngine.processInjectMocks(InjectingAnnotationEngine.java:62)
  at org.mockito.internal.configuration.InjectingAnnotationEngine.process(InjectingAnnotationEngine.java:56)
  at org.mockito.MockitoAnnotations.initMocks(MockitoAnnotations.java:108)
  at com.myproject.presentation.UsersListPresenterTest.setUp(UsersListPresenterTest.java:28)
  at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:191)
  at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:176)
  at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:555)
  at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1853)
  </code></pre>
  
  <p>What am I doing wrong?</p>