title: Exception caught by widgets library The following ArgumentError was thrown building HomePageScreen(dirty, state: _HomePageScreenState#3ae53):
body: <p>Hi guys can you help me with this problem ? i just go around and doesn't get the right answer, thank you.</p>
  
  <pre><code>void _submit() {
    final form = formKey.currentState;
    if (form.validate()) {
      form.save();
      print(_username);
      print(_password);
      if (_username == "asdasd") {
        if (_password == "123") {
          Navigator.pushReplacement(
              this.context, MaterialPageRoute(builder: (context) =&gt; App()));
        } else {
          scaffoldKey.currentState.showSnackBar(SnackBar(
            content: Text("login Failed, please re-type properly"),
            backgroundColor: Colors.redAccent,
          )); // SnackBar
        }
      } else {
        scaffoldKey.currentState.showSnackBar(SnackBar(
          content: Text("Login Failed, please re-type properly"),
          backgroundColor: Colors.redAccent,
        ));
      }
    }
  }
  </code></pre>
  
  <hr>
  
  <p><strong>Error Message:</strong></p>
  
  <blockquote>
    <pre class="lang-none prettyprint-override"><code>════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
  The following ArgumentError was thrown building HomePageScreen(dirty, state: _HomePageScreenState#3ae53):
  Invalid argument(s)
  
  The relevant error-causing widget was: 
    HomePageScreen file:///Users/andrehendrawan/Downloads/ican/lib/Screens/App.dart:20:5
  When the exception was thrown, this was the stack: 
  #0      _StringBase.+ (dart:core-patch/string_patch.dart:265:57)
  #1      _HomePageScreenState._greetings (package:ican/Screens/homePageScreen.dart:237:19)
  #2      _HomePageScreenState.build (package:ican/Screens/homePageScreen.dart:75:17)
  #3      StatefulElement.build (package:flutter/src/widgets/framework.dart:4334:27)
  #4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4223:15)
  ...
  </code></pre>
  </blockquote>