title: view.findViewById returns null,which lead to the " Target must not be null" error by using Picasso
body: <p>I'm using picasso to load pics from web to my app's drawer menu.
  But now I got a problem which I've been trapped in for whole day
  here is my xml:</p>
  
  <pre><code>&lt;/FrameLayout&gt;`&lt;FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:background="@android:color/transparent"
  android:clickable="true"&gt;
  &lt;LinearLayout
      android:id="@+id/vGlobalMenuHeader"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"&gt;
  
      &lt;ImageView
          android:id="@+id/ivMenuUserProfilePhoto"
          android:layout_width="@dimen/global_menu_avatar_size"
          android:layout_height="@dimen/global_menu_avatar_size"
          android:layout_margin="12dp" /&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p></p>
  
  <p>Here is my Java file:</p>
  
  <pre><code>public class MyMenuFragment extends MenuFragment {
  
  private ImageView ivMenuUserProfilePhoto;
  
  @Override
  public void onCreate(@Nullable Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
  }
  
  
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
      View view = inflater.inflate(R.layout.fragment_menu, container,
              false);
      ivMenuUserProfilePhoto = (ImageView)view.findViewById(R.id.ivMenuUserProfilePhoto);
      setupHeader();
      return setupReveal(view) ;
  }
  
  private void setupHeader() {
      int avatarSize = getResources().getDimensionPixelSize(R.dimen.global_menu_avatar_size);
      String profilePhoto = getResources().getString(R.string.user_profile_photo);
      Picasso.with(getActivity())
              .load(profilePhoto)
              .placeholder(R.drawable.img_circle_placeholder)
              .resize(avatarSize, avatarSize)
              .centerCrop()
              .transform(new CircleTransformation())
              .into(ivMenuUserProfilePhoto);
  }
  </code></pre>
  
  <p>Now when I run this project , the console reports the error" Caused by: java.lang.IllegalArgumentException: Target must not be null."</p>
  
  <p>I debugged, found that the <strong>ivMenuUserProfilePhoto indeed is null</strong>, but I don't know why.how come that the findviewById doesn't work?</p>