title: Flutter Provider.of<MyProvider>(...) returns null
body: <p>I have a problem with <code>ChangeNotifierProxyProvider</code>.</p>
  <p>I have a list of providers like</p>
  <pre><code> providers: [
          ChangeNotifierProvider.value(
            value: Auth(),
          ),
          ChangeNotifierProxyProvider&lt;Auth, MyProvider&gt;(
              create: (context) =&gt; MyProvider(),
              update: (ctx, auth, myProvider) =&gt; myProvider.update(auth)),
        ],
  </code></pre>
  <p>If I call <code>Provider.of&lt;MyProvider&gt;(context, listen: false);</code> or <code>context.read&lt;MyProvider&gt;();</code> in my classes I got a null object.</p>
  <p>In another case, if I replace <code>ChangeNotifierProxyProvider</code> to <code>ChangeNotifierProvider</code> (without proxy), I got my provider object.</p>
  <p>I didn't find any similar questions. So I guess I miss something.</p>