title: How to hide thumb on flutter Slider Widget?
body: <p>I have to hide the thumb on Slider widget. I set thumb colour to transparent with SliderTheme widget. It does not work.  How to hide thumb?</p>
  
  <p>I set thumb colour to transparent. </p>
  
  <pre><code>Center(
    child: SliderTheme(
      child: Slider(
        value: 50,
        max: 100,
        min: 0,
        activeColor: Colors.black,
        inactiveColor: Colors.grey,
        onChanged: (double value) {},
      ),
      data: SliderTheme.of(context).copyWith(
        trackHeight: 28, 
        thumbColor: Colors.transparent, 
        thumbShape: null),
    ),
  )
  
  </code></pre>
  
  <p>I expect the slider widget without thumb.</p>