title: java.lang.NullPointerException on clearAnimation()
body: <p>How this crash is possible? It works 99% of the time and sometimes there is this crash...</p>
  
  <pre><code>Caused by java.lang.NullPointerException
  Attempt to invoke virtual method 'void android.view.View.clearAnimation()' on a null object reference
  com.XXX.VerticalPagerFragment.onViewPagerTouchDown
  
  private void onViewPagerTouchDown() {
          if (isAdded()) {
              mPageIndicatorLayout.clearAnimation(); &lt;&lt;&lt; CRASH
              ...
          }
      }
  </code></pre>
  
  <p>Object <code>mPageIndicatorLayout</code> is mapped with butterknife:</p>
  
  <pre><code>@BindView(R2.id.page_indicator_layout)
      View mPageIndicatorLayout;
  </code></pre>
  
  <p>This above method is called from this viewpager listener:</p>
  
  <pre><code>@Override
                  public void onPageScrollStateChanged(int state) {
                      super.onPageScrollStateChanged(state);
                      if (isAdded()) {
                          if (state != ViewPager2.SCROLL_STATE_IDLE) {
                              onViewPagerTouchDown(); &lt;&lt;&lt; HERE
  
                          } else {
                              onViewPagerTouchUp();
                          }
                      }
                  }
  </code></pre>
  
  <p>I can't absolutely understand how this crash can occur in this context? Have you got an ideas?</p>
  
  <p>Thank you very much!</p>