Getting Unexptected null value with Responsive datatable Flutter - flutter

Question

I have implemented this widget 'Responsive datatable' to my Flutter web app.
But I am having some issues and getting this error:
The following TypeErrorImpl was thrown building ResponsiveDatatable(dirty, dependencies: [MediaQuery], state: _ResponsiveDatatableState#5acd2):Unexpected null value.
It works and I am getting data inside my Datatable when I scale my browser to tablet size, but when I click on fullscreen the error shows.
Here is the my code:
class UsersPage extends StatefulWidget {
static const String id = "users_page";
UsersPage({Key? key}) : super(key: key);
#override
_UsersPageState createState() => _UsersPageState();
}
class _UsersPageState extends State<UsersPage> {
late List<DatatableHeader> _headers;
List<int> _perPages = [5, 10, 15, 100];
int _total = 100;
int? _currentPerPage = 5;
int _currentPage = 1;
bool _isSearch = false;
List<Map<String, dynamic>> _source = [];
List<Map<String, dynamic>> _selecteds = [];
String _selectableKey = "id";
String? _sortColumn;
bool _sortAscending = true;
bool _isLoading = true;
bool _showSelect = true;
UserServices _userServices = UserServices();
List<UserModel> _users = <UserModel>[];
List<UserModel> get users => _users;
Future _loadFromFirebase() async {
_users = await _userServices.getAllUsers();
}
List<Map<String, dynamic>> _getUsersData() {
_isLoading = true;
List<Map<String, dynamic>> temps = [];
var i = _users.length;
print(i);
// ignore: unused_local_variable
for (UserModel userData in _users) {
print(userData.name);
print(userData.email);
temps.add({
"id": userData.uid,
"email": userData.email,
"name": userData.name,
});
i++;
}
return temps;
}
_initializeData() async {
_isLoading = true;
await _loadFromFirebase();
_source.addAll(_getUsersData());
print(_source);
}
onSort(dynamic value) {
_sortColumn = value;
_sortAscending = !_sortAscending;
if (_sortAscending) {
_source
.sort((a, b) => b["$_sortColumn"].compareTo(a["$_sortColumn"]));
} else {
_source
.sort((a, b) => a["$_sortColumn"].compareTo(b["$_sortColumn"]));
}
}
onChanged(int value) {
_currentPerPage = value;
}
previous() {
_currentPage = _currentPage >= 2 ? _currentPage - 1 : 1;
}
next() {
_currentPage++;
}
#override
void initState() {
super.initState();
/// set headers
_headers = [
DatatableHeader(
text: "ID",
value: "id",
show: true,
sortable: true,
textAlign: TextAlign.center),
DatatableHeader(
text: "Name",
value: "name",
show: true,
flex: 2,
sortable: true,
editable: true,
textAlign: TextAlign.left),
DatatableHeader(
text: "SKU",
value: "email",
show: true,
sortable: true,
textAlign: TextAlign.center),
];
_initializeData();
}
#override
void dispose() {
super.dispose();
}
#override
Widget build(BuildContext context) {
return SingleChildScrollView(
child: Column(
mainAxisAlignment: MainAxisAlignment.start,
mainAxisSize: MainAxisSize.max,
children: [
Container(
margin: EdgeInsets.all(10),
padding: EdgeInsets.all(0),
constraints: BoxConstraints(
maxHeight: 700,
),
child: Card(
elevation: 1,
shadowColor: Colors.black,
clipBehavior: Clip.none,
child: ResponsiveDatatable(
title: !_isSearch
? ElevatedButton.icon(
onPressed: () {},
icon: Icon(Icons.add),
label: Text("ADD CATEGORY")) : null,
actions: [
if (_isSearch)
Expanded(
child: TextField(
decoration: InputDecoration(
prefixIcon: IconButton(
icon: Icon(Icons.cancel),
onPressed: () {
setState(() {
_isSearch = false;
});
}),
suffixIcon: IconButton(
icon: Icon(Icons.search), onPressed: () {})),
)),
if (!_isSearch)
IconButton(
icon: Icon(Icons.search),
onPressed: () {
setState(() {
_isSearch = true;
});
})
],
headers: _headers,
source: _source,
selecteds: _selecteds,
showSelect: _showSelect,
autoHeight: true,
onTabRow: (data) {
print(data);
},
onSort: onSort,
sortAscending: _sortAscending,
sortColumn: _sortColumn,
isLoading: _isLoading,
onSelect: (value, item) {
print("$value $item ");
if (value!) {
setState(() => _selecteds.add(item));
} else {
setState(
() => _selecteds.removeAt(_selecteds.indexOf(item)));
}
},
onSelectAll: (value) {
if (value!) {
setState(() => _selecteds =
_source.map((entry) => entry).toList().cast());
} else {
setState(() => _selecteds.clear());
}
},
footers: [
Container(
padding: EdgeInsets.symmetric(horizontal: 15),
child: Text("Rows per page:"),
),
if (_perPages != null)
Container(
padding: EdgeInsets.symmetric(horizontal: 15),
child: DropdownButton(
value: _currentPerPage,
items: _perPages
.map((e) => DropdownMenuItem(
child: Text("$e"),
value: e,
))
.toList(),
onChanged: (value) {}),
),
Container(
padding: EdgeInsets.symmetric(horizontal: 15),
child: Text(
"${_currentPage} - ${_currentPage} of ${_total}"),
),
IconButton(
icon: Icon(
Icons.arrow_back_ios,
size: 16,
),
onPressed: previous,
padding: EdgeInsets.symmetric(horizontal: 15),
),
IconButton(
icon: Icon(Icons.arrow_forward_ios, size: 16),
onPressed: next,
padding: EdgeInsets.symmetric(horizontal: 15),
)
],
),
),
),
],
),
);
}
}