title: Flutter Remove bottom underline from DropDropdownButton
body: <p>I have a drop down menu that is positioned in my app bar. However it seems to have default with an underline. The flutter docs say that is defaults to 0.0 which cant be the case and I can see the underline. How do I remove this underline. </p>
  
  <pre><code>return Container(
    decoration: BoxDecoration(
      color: Colors.white,
      borderRadius: BorderRadius.all(Radius.circular(30)),
    ),
    margin: EdgeInsets.all(10.0),
    padding: EdgeInsets.all(5.0),
    width: MediaQuery.of(context).size.width * 0.30,
    child: Center(
      child: DropdownButton(
        items: _dropdownValues.map((value) =&gt; DropdownMenuItem(child: Text(value), value: value)).toList(),
          onChanged: (String value) {
            setState(() {
              _currentlySelected = value;
            });
          },
        isExpanded: false,
        value: _currentlySelected,
      )
    )
  ); 
  </code></pre>
  
  <p><strong>Design:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/nncgG.png" rel="noreferrer"><img src="https://i.stack.imgur.com/nncgG.png" alt="enter image description here"></a></p>