title: Null pointer exception in ExpandableListView
body: <p>I have the attached exception when I try to make a ExpandableListView</p>
  
  <p>can anyone help!</p>
  
  <p><img src="https://i.stack.imgur.com/mwclV.png" alt="enter image description here"></p>
  
  <p>this is my method </p>
  
  <pre><code>@Override
      public View getChildView(int groupPosition, int childPosition,
              boolean isLastChild, View convertView, ViewGroup parent) {
  
          View childView;
  
          if (convertView == null) {
  
              LayoutInflater infalInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
              childView = infalInflater.inflate(R.layout.side_menu_child_view,null);
          } else {
              childView = convertView;
          }
  
          TextView linkName       = (TextView) childView.findViewById(R.id.child_title_text);
          LinkEntity linkEntity   = getChild(groupPosition, childPosition);
          linkName.setText(linkEntity.getDisplayName(true));
          return childView;
      }
  </code></pre>
  
  <p>this is the xml of my list </p>
  
  <p>
  </p>
  
  <pre><code>&lt;EditText
      android:id="@+id/search_edit_text"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:inputType="text"
      android:visibility="gone" /&gt;
  
  &lt;ExpandableListView
      android:id="@+id/expandable_side_list_view"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:cacheColorHint="@android:color/transparent"
      android:childDivider="@null"
      android:childIndicator="@null"
      android:divider="@drawable/side_menu_separator"
      android:dividerHeight="0dp"
      android:groupIndicator="@null"
      android:listSelector="@android:color/transparent" &gt;
  &lt;/ExpandableListView&gt;
  </code></pre>
  
  <p></p>