title: Flutter Error: Another exception was thrown: Instance of 'DiagnosticsProperty<void>' .It is showing a blank screen when redirected to that page
body: <p>Flutter Error: Another exception was thrown: Instance of 'DiagnosticsProperty' .It is showing a blank screen when redirected to that page.</p>
  <p>I have successfully uploaded the text items , one image and one pdf to the firebase database and able to retrieve all of them in cards Widget view and List Tiles View Now I am trying to get individual view when clicked on List Items from List view.</p>
  <p>Please check my code , I am seeing a blank screen when tried to redirect to the required Retrievepage.</p>
  <pre><code>                                  RetrievePage.dart
  
  
                                       
  import 'dart:async';
  import 'dart:io';
  import 'package:firebase_auth/firebase_auth.dart';
  import 'package:firebase_database/firebase_database.dart';
  import 'package:flutter/material.dart';
  import 'package:fluttertoast/fluttertoast.dart';
  import 'package:gadjet_inventory/Form/ListTileFeed.dart';
  import 'package:gadjet_inventory/Form/ListTiles.dart';
  import 'package:gadjet_inventory/main.dart';
  import 'package:intl/intl.dart';
  import 'package:gadjet_inventory/Form/Data.dart';
  
  
  import 'package:gadjet_inventory/Form/UploadData.dart';
  
  import 'package:pdf_flutter/pdf_flutter.dart';
  // ignore: must_be_immutable
  import 'package:url_launcher/url_launcher.dart';
  
  import 'Data.dart';
  
  class RetrievePage extends StatefulWidget {
  
  //  String currentEmail;
  
    //RetrievePage(this.currentEmail);
  
    @override
    _RetrievePageState createState() =&gt; _RetrievePageState();
  }
  
  class _RetrievePageState extends State&lt;RetrievePage&gt; {
    List&lt;Data&gt; dataList = [];
    List&lt;bool&gt; favList = [];
    bool searchState = false;
    FirebaseAuth auth = FirebaseAuth.instance;
  
  
  
  
  
    @override
    void initState() {
      // TODO: implement initState
      super.initState();
      DatabaseReference referenceData = FirebaseDatabase.instance.reference().child(&quot;Data&quot;);
      referenceData.once().then((DataSnapshot dataSnapShot) {
        dataList.clear();
        favList.clear();
  
        var keys = dataSnapShot.value.keys;
        var values = dataSnapShot.value;
  
        for (var key in keys) {
  
          Data data = new Data(
              values [key]['imgUrl'],
            
              values [key]['cattegorrytype'],
              values [key]['companyname'],
              values [key]['modelname'],
              values [key]['seriesname'],
              values [key]['serielnumber'],
              values [key]['year'],
              
  
              key
            //key is the uploadid
          );
          dataList.add(data);
          auth.currentUser().then((value) {
            DatabaseReference reference = FirebaseDatabase.instance.reference().child(&quot;Data&quot;).child(key).child(&quot;Fav&quot;)
                .child(value.uid).child(&quot;state&quot;);
            reference.once().then((DataSnapshot snapShot){
              if(snapShot.value!=null){
                if(snapShot.value==&quot;true&quot;){
                  favList.add(true);
                }else{
                  favList.add(false);
                }
              }else{
                favList.add(false);
              }
            });
          });
  
        }
  
  
        Timer(Duration(seconds: 1),(){
          setState(() {
            //
          });
        });
  
  
      });
  
  
    }
  
  
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        appBar: AppBar(
          title: Text(
            &quot;List View&quot;,
          ),
          actions: &lt;Widget&gt;[
            // action button
  
          ],
        ),
        body: Center(
  
          child: Container(
           child: ListView.separated(
          itemBuilder: (BuildContext context, int index) {
          Column(
              children: &lt;Widget&gt;[
                Image.network(
                  dataList[index].imgUrl != null
                      ? dataList[index].imgUrl
                      : '',
                  width: 500,
                  height: 500,
  
                ),
  
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: &lt;Widget&gt;[
                    Expanded(
                      flex: 1,
                      child: Padding(
                        padding: const EdgeInsets.all(8.0),
  
                            child: Text(  &quot;Cattegorry Type:- &quot;
                            &quot;$dataList[index].cattegorrytype&quot;,
  
                             style: TextStyle(color: Colors.black),
  
   
                        ),
  
  
                      ),
                    ),
                  ],
                ),
  
  
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: &lt;Widget&gt;[
                    Expanded(
                      flex: 1,
                      child: Padding(
                        padding: const EdgeInsets.all(8.0),
                        child: Theme(
                          data: ThemeData(
                            hintColor: Colors.blue,
                          ),
  
                          child: Text(  &quot;Company Name:- &quot;
                              &quot;$dataList[index].companyname&quot;,
     
                            style: TextStyle(color: Colors.black),
  
                              ),
                        ),
                      ),
                    ),
    
  
                    Expanded(
                      flex: 1,
                      child: Padding(
                        padding: const EdgeInsets.all(8.0),
                        child: Theme(
                          data: ThemeData(
                            hintColor: Colors.blue,
                          ),
  
                          child: Text(  &quot;Model Name:- &quot;
                              &quot;$dataList[index].modelname&quot;,
  
                               style: TextStyle(color: Colors.black),
     
                          ),
                        ),
                      ),
                    ),
  
                  ],
                ),
  
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: &lt;Widget&gt;[
                    Expanded(
                      flex: 1,
                      child: Padding(
                        padding: const EdgeInsets.all(8.0),
                        child: Theme(
                          data: ThemeData(
                            hintColor: Colors.blue,
                          ),
  
                          child: Text(  &quot;Series Name:- &quot;
                              &quot;$dataList[index].seriesname&quot;,
  
                               style: TextStyle(color: Colors.black),
  
    
                          ),
                      ),
                      ),
                    ),
     
                    Expanded(
                      flex: 1,
                      child: Padding(
                        padding: const EdgeInsets.all(8.0),
                        child: Theme(
                          data: ThemeData(
                            hintColor: Colors.blue,
                          ),
  
                          child: Text(  &quot;Year Of MFG:- &quot;
                              &quot;$dataList[index].year&quot;,
    
  
                            style: TextStyle(color: Colors.black),
  
     
                          ),
                        ),
                      ),
                    ),
  
                  ],
                ),
  
                 
              ],
          );
          },
         ),
          ),
  
  
        ),
  
  
  
  
  
      );
    }
      
    }
  </code></pre>
  <p>Please fix my issue why I am seeing a blank screen with the error &quot;Another exception was thrown: Instance of 'DiagnosticsProperty'&quot;</p>