title: use of HexEncoder class from flutter
body: <p>I am trying to use the class HexEncoder from <a href="https://docs.flutter.io/flutter/convert/HexEncoder-class.html" rel="noreferrer">https://docs.flutter.io/flutter/convert/HexEncoder-class.html</a> and i can't make it work. Actually i am doing this to convert a list of bytes to a string:</p>
  
  <pre><code>import 'dart:convert';
  import 'package:convert/convert.dart';
  
  HexEncoder _hexEncoder;
  List&lt;int&gt; value = [253, 165, 6, 147, 164, 226, 79, 177, 175, 207, 198, 235, 7, 100, 120, 37]
  _hexEncoder.convert(value);
  </code></pre>
  
  <p>but throws me the error:</p>
  
  <pre><code> The method 'convert' was called on null
  </code></pre>
  
  <p>Sorry for my poor knowledge of dart/flutter. I know i amb calling a null object, i just need to know the way to use this class. Thank you so much !</p>