The getter 'navigator' was called on null

Question

Since this morning I have been getting this error, after looking at the stack trace, I have traced the error back to the runApp method, I don't understand at all, what the problem is, any help would be appreciated :) This is the exception: The getter 'navigator' was called on null

Here is my main.dart file

import 'dart:async';
import 'package:firebase_analytics/firebase_analytics.dart';
import 'package:firebase_analytics/observer.dart';
import 'package:flutter/material.dart';
import 'package:savings/utils/analytics.dart';
import 'package:savings/utils/colors.dart';
import 'package:savings/pages/goals_page.dart';
import 'package:savings/utils/logic.dart' as AppLogic;
import 'package:savings/utils/models.dart' as models;
import 'package:savings/utils/variables.dart';
import 'package:flutter/services.dart';

void main() => runApp(new SavingsApp());

class SavingsApp extends StatefulWidget {
 @override
 _SavingsAppState createState() => new _SavingsAppState();
}

class _SavingsAppState extends State<SavingsApp> {
 @override
 void initState() {
 initAppData();
 super.initState();
}

 @override
 Widget build(BuildContext context) {
  return new MaterialApp(
  debugShowCheckedModeBanner: false,
  title: 'Savings',
  color: primaryThemeColor,
  home: GoalsPage(),
  navigatorObservers: <NavigatorObserver>[analyticsObserver],
  theme: new ThemeData(
    primaryColor: primaryThemeColor,
    accentColor: accentThemeColor,
    fontFamily: "Proxima Nova",
  ),
);
}

@override
void dispose() {
 //Good practice to close the DB
 AppLogic.DatabaseInterface.closeDB();

//Handle orientation
SystemChrome.setPreferredOrientations([
  DeviceOrientation.landscapeRight,
  DeviceOrientation.landscapeLeft,
  DeviceOrientation.portraitUp,
  DeviceOrientation.portraitDown,
]);
super.dispose();
}

 Future<Null> initAppData() async {

//Database
_initDBData();

//Analytics
analytics = new FirebaseAnalytics();
AnalyticsInterface.logAppOpen();
analyticsObserver = new FirebaseAnalyticsObserver(analytics: analytics);
  }

  Future<Null> _initDBData() async {
   //Orientation
    SystemChrome.setPreferredOrientations([
      DeviceOrientation.portraitUp,
    ]);

//Retrieve database from the DB interface
appDatabase = await AppLogic.DatabaseInterface.getDB();

//Log output
print("DatabaseInterface: DatabaseInitiated");

//Get a local version of the lists after the DB has been initiated
List<models.Goal> _goalsList =
    await AppLogic.DatabaseInterface.getAllGoalsFromDB();

List<models.Transaction> _transactionsList =
    await AppLogic.DatabaseInterface.getAllTransactionsFromDB();

//Call setState and update the global lists (which are used in the whole app) from the local ones
setState(() {
  allGoalsList = _goalsList;
  allTransactionsList = _transactionsList;
    });
  }
}

Logcat

The following NoSuchMethodError was thrown building 
DefaultTextStyle(debugLabel: fallback style;
I/flutter ( 4211): consider putting your text in a Material, inherit: true, 
color: Color(0xd0ff0000), family:
I/flutter ( 4211): monospace, size: 48.0, weight: 900, decoration: double 
Color(0xffffff00) TextDecoration.underline,   
I/flutter ( 4211): softWrap: wrapping at box width, overflow: clip):
I/flutter ( 4211): The getter 'navigator' was called on null.
I/flutter ( 4211): Receiver: null
I/flutter ( 4211): Tried calling: navigator
I/flutter ( 4211): 
I/flutter ( 4211): When the exception was thrown, this was the stack:
I/flutter ( 4211): #0      Object.noSuchMethod 
(dart:core/runtime/libobject_patch.dart:46:5)
I/flutter ( 4211): #1      NavigatorState.initState 
(package:flutter/src/widgets/navigator.dart:1303:23)
I/flutter ( 4211): #2      StatefulElement._firstBuild 
(package:flutter/src/widgets/framework.dart:3751:58)
I/flutter ( 4211): #3      ComponentElement.mount 
(package:flutter/src/widgets/framework.dart:3617:5)
...
...
I/flutter ( 4211): #104    runApp (package:flutter/src/widgets/binding.dart:704:7)
I/flutter ( 4211): #105    main (file:///C:/Coding/savings/lib/main.dart:13:16)
I/flutter ( 4211): #106    _startIsolate.<anonymous closure (dart:isolate/runtime/libisolate_patch.dart:279:19)
I/flutter ( 4211): #107    _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:165:12)

Answer 1

You are getting this error because, the navigatorObserver instance "analyticsObserver" you are passing in your navigationObservers array is being instantiated in an async function, means, possibly when the build function is running for the first time, that time your "analyticsObserver" is null.

Try adding the following condition while assigning your navigationObservers array

navigatorObservers: (null == analyticsObserver)? [] : <NavigatorObserver>[analyticsObserver],

Or simply return circular progress indicator while analyticsObserver is null.