User called to null when trying to user the search screen

[jeremiahseun]

I have loaded the project and there is no error. But when I want to open the search screen for me to search for other users, it brings an error of "User call to null"

This is my Search Screen

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:scrolly/models/user.dart' as user;
import 'package:scrolly/resources/firebase_repository.dart';
import 'package:scrolly/screens/chat_screen.dart';
import 'package:scrolly/screens/widgets/custom_tile.dart';
import 'package:scrolly/utils/universal_variables.dart';

class SearchScreen extends StatefulWidget {
  @override
  _SearchScreenState createState() => _SearchScreenState();
}

class _SearchScreenState extends State<SearchScreen> {
  final FirebaseRepository _firebaseRepository = FirebaseRepository();

  List<User> userList;
  String query = "";
  TextEditingController searchController = TextEditingController();
  FirebaseAuth auth = FirebaseAuth.instance;

  @override
  void initState() {
    super.initState();

    _firebaseRepository.getCurrentUser().then((User user) {
      _firebaseRepository.fetchAllUsers(user).then((List<User> list) {
        setState(() {
          userList = list;
        });
      });
    });
  }

  searchAppBar(BuildContext context) {
    return AppBar(
      leading: IconButton(
        icon: Icon(Icons.arrow_back, color: Colors.white),
        onPressed: () => Navigator.pop(context),
      ),
      elevation: 10,
      bottom: PreferredSize(
        preferredSize: const Size.fromHeight(kToolbarHeight + 20),
        child: Padding(
          padding: EdgeInsets.only(left: 20),
          child: TextField(
            controller: searchController,
            onChanged: (val) {
              setState(() {
                query = val;
              });
            },
            cursorColor: UniversalVariables.blackColor,
            autofocus: true,
            style: TextStyle(
              fontWeight: FontWeight.bold,
              color: Colors.white,
              fontSize: 35,
            ),
            decoration: InputDecoration(
              suffixIcon: IconButton(
                icon: Icon(Icons.close, color: Colors.white),
                onPressed: () {
                  WidgetsBinding.instance
                      .addPostFrameCallback((_) => searchController.clear());
                },
              ),
              border: InputBorder.none,
              hintText: "Search",
              hintStyle: TextStyle(
                fontWeight: FontWeight.bold,
                fontSize: 35,
                color: Color(0x88ffffff),
              ),
            ),
          ),
        ),
      ),
    );
  }

  buildSuggestions(String query) {
    final List<User> suggestionList = query.isEmpty
        ? []
        : userList != null
            ? userList.where((user) {
                String _getUsername = user.email.toLowerCase();
                String _query = query.toLowerCase();
                String _getName = user.displayName.toLowerCase();
                bool matchesUsername = _getUsername.contains(_query);
                bool matchesName = _getName.contains(_query);

            return (matchesUsername || matchesName);

            // (User user) => (user.username.toLowerCase().contains(query.toLowerCase()) ||
            //     (user.name.toLowerCase().contains(query.toLowerCase()))),
          }).toList()
        : [];

return ListView.builder(
  itemCount: suggestionList.length,
  itemBuilder: ((context, index) {
    User searchedUser = user.UUser(
        uid: suggestionList[index].uid,
        profilePhoto: suggestionList[index].photoURL,
        name: suggestionList[index].displayName,
        username: suggestionList[index].email) as User;

    return CustomTile(
      mini: false,
      onTap: () {
        Navigator.push(
            context,
            MaterialPageRoute(
                builder: (context) => ChatScreen(
                      receiver: searchedUser,
                    )));
      },
      leading: CircleAvatar(
        backgroundImage: NetworkImage(searchedUser.photoURL),
        backgroundColor: Colors.grey,
      ),
      title: Text(
        searchedUser.email,
        style: TextStyle(
          color: Colors.white,
          fontWeight: FontWeight.bold,
        ),
      ),
      subtitle: Text(
        searchedUser.displayName,
        style: TextStyle(color: UniversalVariables.greyColor),
      ),
    );
  }),
);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: UniversalVariables.blackColor,
      appBar: searchAppBar(context),
      body: Container(
        padding: EdgeInsets.symmetric(horizontal: 20),
        child: buildSuggestions(query),
      ),
    );
  }
}

USER MODEL CLASS

class UUser {
  String uid;
  String name;
  String email;
  String username;
  String status;
  int state;
  String profilePhoto;

  UUser({
    this.uid,
    this.name,
    this.email,
    this.username,
    this.status,
    this.state,
    this.profilePhoto,
  });

  Map toMap(UUser user) {
    var data = Map<String, dynamic>();
    data['uid'] = user.uid;
    data['name'] = user.name;
    data['email'] = user.email;
    data['username'] = user.username;
    data["status"] = user.status;
    data["state"] = user.state;
    data["profile_photo"] = user.profilePhoto;
    return data;
   }

  // Named constructor
  UUser.fromMap(Map<String, dynamic> mapData) {
    this.uid = mapData['uid'];
    this.name = mapData['name'];
    this.email = mapData['email'];
    this.username = mapData['username'];
    this.status = mapData['status'];
    this.state = mapData['state'];
    this.profilePhoto = mapData['profile_photo'];
  }
}

FIREBASE METHODS CLASS

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:firebase_storage/firebase_storage.dart';
import 'package:flutter/material.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'package:scrolly/constants/strings.dart';
import 'package:scrolly/models/post.dart';
import 'package:scrolly/models/user.dart' as user;
import 'package:scrolly/utils/utilities.dart';

class FirebaseMethods {
  final FirebaseAuth _auth = FirebaseAuth.instance;

  final GoogleSignIn _googleSignIn = GoogleSignIn();
  static final FirebaseFirestore firestore = FirebaseFirestore.instance;

  final FirebaseStorage firebaseStorage = FirebaseStorage.instance;

  //user class
  var user;

  Future<User> getCurrentUser() async {
    User currentUser;
    currentUser = _auth.currentUser;
    return currentUser;
  }

  Future<User> signIn() async {
    try {
      final GoogleSignInAccount _signInAccount = await _googleSignIn.signIn();
      final GoogleSignInAuthentication _signInAuthentication =
          await _signInAccount.authentication;

  final AuthCredential credential = GoogleAuthProvider.credential(
    accessToken: _signInAuthentication.accessToken,
    idToken: _signInAuthentication.idToken,
  );

  User user = (await _auth.signInWithCredential(credential)).user;
  return user;
} catch (e) {
  print(e);
}
return null;
  }

  Future<bool> authenticateUser(User user) async {
    QuerySnapshot result = await firestore
        .collection('users')
        .where('email', isEqualTo: user.email)
        .get();

final List<DocumentSnapshot> docs = result.docs;

//if user is registered then length of lost > 0 else less than 0
return docs.length == 0 ? true : false;
  }

  Future<void> addDataToDb(User currentUser) async {
    String username = Utils.getUsername(currentUser.email);
    user = user.UUser(
        uid: currentUser.uid,
        email: currentUser.email,
        name: currentUser.displayName,
        profilePhoto: currentUser.photoURL,
        username: username);

firestore.collection('users').doc(currentUser.uid).set(user.toMap(user));
  }

  Future<Post> addPostToDb(Post post) async {
    post = Post(
      uid: user.uid,
      caption: post.caption,
     name: post.name,
      photoUrl: post.photoUrl,
       date: DateTime.now().toString(),
    );

firestore.collection('posts').doc(user.uid).set(
      post.toMap(post),
    );
return null;
  }

  Future<void> signOut() async {
    await _googleSignIn.disconnect();
    await _googleSignIn.signOut();
    return await _auth.signOut();
  }

  static final FirebaseFirestore _firestore = FirebaseFirestore.instance;

  static final CollectionReference _userCollection =
      _firestore.collection(USERS_COLLECTION);

  Future<User> getUserDetails() async {
    FirebaseAuth auth = FirebaseAuth.instance;

DocumentSnapshot documentSnapshot =
    await _userCollection.doc(auth.currentUser.uid).get();
return user.User.map(documentSnapshot.data);
  }

  Future<User> getUserDetailsById(id) async {
    try {
      DocumentSnapshot documentSnapshot = await _userCollection.doc(id).get();
      return user.User.fromMap(documentSnapshot.data);
    } catch (e) {
     print(e);
      return null;
    }
  }

  Stream<DocumentSnapshot> getUserStream({@required String uid}) =>
      _userCollection.doc(uid).snapshots();

  Future<List<User>> fetchAllUsers(User currentUser) async {
    List<User> userList = List<User>();

    QuerySnapshot querySnapshot =
        await firestore.collection(USERS_COLLECTION).get();
    for (var i = 0; i < querySnapshot.docs.length; i++) {
      if (querySnapshot.docs[i].id != currentUser.uid) {
        userList.add(user.User.fromMap(querySnapshot.docs[i].data));
      }
    }
    return userList;
  }
}

FIREBASE REPOSITORY CLASS

import 'package:scrolly/models/post.dart';
import 'package:scrolly/resources/firebase_methods.dart';
import 'package:firebase_auth/firebase_auth.dart';

class FirebaseRepository {
  FirebaseMethods _firebaseMethods = FirebaseMethods();

  Future<User> getCurrentUser() => _firebaseMethods.getCurrentUser();

  Future<User> signIn() => _firebaseMethods.signIn();

  Future<bool> authenticateUser(User user) =>
      _firebaseMethods.authenticateUser(user);

  Future<void> addDataToDb(User user) => _firebaseMethods.addDataToDb(user);

  Future<Post> addPostToDb(Post post) => _firebaseMethods.addPostToDb(post);

  Future<void> signOut() => _firebaseMethods.signOut();

  Future<List<User>> fetchAllUsers(User user) =>
      _firebaseMethods.fetchAllUsers(user);
 }

AND THE EXCEPTION ERROR FROM TERMINAL WHEN I OPEN THE SEARCH SCREEN

2 W/com.scrolly.ap(17540): Accessing hidden method Lsun/misc/Unsafe;->getObject(Ljava/lang/Object;J)Ljava/lang/Object; 
(greylist, linking, allowed) W/com.scrolly.ap(17540): Accessing hidden method Lsun/misc/Unsafe;->getInt(Ljava/lang/Object;J)I 
(greylist, linking, allowed) W/com.scrolly.ap(17540): 
Accessing hidden method Lsun/misc/Unsafe;- 

getObject(Ljava/lang/Object;J)Ljava/lang/Object; (greylist, linking, allowed) I/chatty (17540): uid=10517(com.scrolly.app)
FirestoreWorker identical 1 line 2 W/com.scrolly.ap(17540):
Accessing hidden method Lsun/misc/Unsafe;-
getObject(Ljava/lang/Object;J)Ljava/lang/Object; (greylist, linking, allowed) W/com.scrolly.ap(17540): Accessing hidden
method Lsun/misc/Unsafe;->putObject(Ljava/lang/Object;JLjava/lang/Object;)V (greylist, linking, allowed)
W/com.scrolly.ap(17540):
Accessing hidden method Lsun/misc/Unsafe;->getInt(Ljava/lang/Object;J)I (greylist, linking, allowed)
W/com.scrolly.ap(17540):
Accessing hidden method Lsun/misc/Unsafe;->getObject(Ljava/lang/Object;J)Ljava/lang/Object;
(greylist, linking, allowed) W/com.scrolly.ap(17540): Accessing hidden method Lsun/misc/Unsafe;-
>putInt(Ljava/lang/Object;JI)V (greylist, linking, allowed)
E/flutter (17540): [ERROR:flutter/lib/ui/ui_dart_state.cc(177)]
Unhandled Exception: NoSuchMethodError: The getter 'User' was called on null.
E/flutter (17540): Receiver: null E/flutter
(17540): Tried calling: User E/flutter (17540): #0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5) E/flutter
(17540): #1 FirebaseMethods.fetchAllUsers package:scrolly/resources/firebase_methods.dart:125 E/flutter (17540): E/flutter
(17540): #2 FirebaseRepository.fetchAllUsers package:scrolly/resources/firebase_repository.dart:22 E/flutter (17540): #3
_SearchScreenState.initState. package:scrolly/…/search/search_screen.dart:27 E/flutter (17540): #4 _rootRunUnary
(dart:async/zone.dart:1198:47) E/flutter (17540): #5 _CustomZone.runUnary (dart:async/zone.dart:1100:19) E/flutter (17540): #6
_FutureListener.handleValue (dart:async/future_impl.dart:143:18) E/flutter (17540): #7
Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:696:45) E/flutter (17540): #8
Future._propagateToListeners (dart:async/future_impl.dart:725:32) E/flutter (17540): #9 Future._completeWithValue
(dart:async/future_impl.dart:529:5) E/flutter (17540): #10 Future._asyncCompleteWithValue. (dart:async/future_impl.dart:567:7)
E/flutter (17540): #11 _rootRun (dart:async/zone.dart:1190:13) E/flutter (17540): #12 _CustomZone.run
(dart:async/zone.dart:1093:19) E/flutter (17540): #13 _CustomZone.runGuarded (dart:async/zone.dart:997:7) E/flutter (17540):
#14 _CustomZone.bindCallbackGuarded. (dart:async/zone.dart:1037:23) E/flutter (17540): #15 _microtaskLoop
(dart:async/schedule_microtask.dart:41:21) E/flutter (17540): #16 _startMicrotaskLoop
(dart:async/schedule_microtask.dart:50:5) E/flutter (17540): W/com.scrolly.ap(17540): Accessing hidden method
Lsun/misc/Unsafe;->getObject(Ljava/lang/Object;J)Ljava/lang/Object; (greylist, linking, allowed)