title: NullPointerException with AppCompat BottomSheets
body: <pre><code>LinearLayout bottomSheetViewgroup = (LinearLayout) findViewById(R.id.bottomSheet);
  
  bottomSheetBehavior = BottomSheetBehavior.from(bottomSheetViewgroup);
  
  bottomSheetBehavior.setState(BottomSheetBehavior.STATE_EXPANDED); //this line
  </code></pre>
  
  <p>I have this code within my activity's <code>onCreate()</code> method and I'm getting the below NPE exception when the last line is executed:</p>
  
  <blockquote>
    <p>Caused by: java.lang.NullPointerException:
                 Attempt to invoke virtual method 'java.lang.Object java.lang.ref.WeakReference.get()' on a null object reference 
                 at android.support.design.widget.BottomSheetBehavior.setState(BottomSheetBehavior.java:440)</p>
  </blockquote>