title: JMockit NullPointerException on mocked object in Expectations
body: <p>Here is the relevant part of my test case:</p>
  
  <pre><code>@NonStrict
  private StowServiceWrapper mockStowServiceWrapper;
  
  @NonStrict
  private IsItemStowableResponse mockIsItemStowableResponse;
  
  @NonStrict
  private IsItemStowable mockIsItemStowable;
  
  ...
  
  @Test
  public void testMoveItemActivitySuccess() {
      final MoveItemActivity activity = new MoveItemActivity();        
  
      final MoveItemRequest request = new MoveItemRequest();
  
      new Expectations() {
  
          {
              invoke(activity, "isItemStowable", request); result=mockIsItemStowable;
              //activity.isItemStowable(request); result=mockIsItemStowable;
              mockStowServiceWrapper.isItemStowableToBin(anyString, anyString, anyString, anyString); result=mockIsItemStowableResponse;
              mockIsItemStowableResponse.hasFilterResults();result=false;
          }
      };
  
      MoveItemResponse response = activity.enact(request);
  </code></pre>
  
  <p>Here is the relevant part of the class source (in MoveItemActivity):</p>
  
  <pre><code>StowServiceWrapper stowServiceWrapper = new StowServiceWrapperImpl();
  private IsItemStowable isItemStowable(MoveItemRequest input) {
  
      IsItemStowable isStowable = new IsItemStowable();
      isStowable.setIsItemStowable(false);
  
      System.out.println("TEST1");
      /* First check if item is stowable to bin */
      IsItemStowableToBinResponse isItemStowableResponse = stowServiceWrapper.isItemStowableToBin();
      System.out.println("TEST2");
      /* fastFail is 'true' by default, so stow service request will only return one filter violation at a time */
      if (isItemStowableResponse.hasFilterResults()) {
          ...
      }
  </code></pre>
  
  <p>I'm getting a NullPointerException at this line: <code>if (isItemStowableResponse.hasFilterResults())</code></p>
  
  <p>I'm relatively new to JMockit.  I'm not sure why it's executing the code inside this method - I just want to mock the whole method since it's a dependency in my 'enact' method which I'm trying to unit test.</p>