title: type 'Null' is not a subtype of type 'String' of 'function result' when update the provider model
body: <p>Provider version and dart</p>
  <pre><code>provider: ^6.0.1
  sdk: &quot;&gt;=2.12.0 &lt;3.0.0&quot;
  </code></pre>
  <p>I have two screens.</p>
  <p>Screen A - I have a form. when you tap on the textbox it will open a Screen B Full screen Modal.</p>
  <p>Screen B - you will choose an item from the list in and return back to Screen A.</p>
  <p>In the Screen A textbox i have wrapped with consumer method.</p>
  <pre><code>Consumer&lt;AgentModel&gt;( //                    &lt;--- Consumer
          builder: (context, agentModel, child) {
            agentController.text = agentModel.name.toString();
            return  AppInputWrapper(
              marginBottom: 'small',
              widgets: Column(
                children: [
                  TextFormField(
                    style: appInputStyle,
                    keyboardType: TextInputType.text,
                    autocorrect: false,
                    enableSuggestions: false,
                    decoration: AppInputStyleDecoration.textFieldStyle(hintTextStr: &quot;Agent&quot;),
                    controller: agentController,
                    validator: (value) {
                      return validateAgent(value);
                    },
                    readOnly: true,
                    onTap: (){
                      Navigator.push(  context, MaterialPageRoute( builder: (context) =&gt; AgentFormComponent(),),);
                    },
                  ),
                ],
              ),
            );
          }
      )
  </code></pre>
  <p>When the first instance it comes from screen B to screen A its not loading the value from provider. i get the following error.</p>
  <pre><code>======== Exception caught by widgets library =======================================================
  The following _TypeError was thrown building Consumer&lt;AgentModel&gt;(dirty, dependencies: [_InheritedProviderScope&lt;AgentModel?&gt;]):
  type 'Null' is not a subtype of type 'String' of 'function result'
  
  The relevant error-causing widget was: 
    Consumer&lt;AgentModel&gt; file:///Users/soundharraj/StudioProjects/LHMarine/lib/screens/jobs/create/form.dart:389:13
  When the exception was thrown, this was the stack: 
  #0      _Location.file (package:flutter/src/widgets/widget_inspector.dart)
  #1      _Location.toJsonMap (package:flutter/src/widgets/widget_inspector.dart:2844:15)
  #2      _Location.toJsonMap.&lt;anonymous closure&gt; (package:flutter/src/widgets/widget_inspector.dart:2853:42)
  #3      MappedListIterable.elementAt (dart:_internal/iterable.dart:412:31)
  #4      ListIterator.moveNext (dart:_internal/iterable.dart:341:26)
  ...
  ====================================================================================================
  Reloaded 1 of 1128 libraries in 592ms.
  </code></pre>
  <p>I am not sure how to check the provider value is NULL. its turn the string.</p>
  <p>Thanks</p>