How to use where method with null boolean - flutter

Question

I have a list like this:
[
{'country': ' Wakanda', 'languages': null},
{
'country': 'USA',
'languages': [
{'language': 'English'}
]
},
{
'country': 'Germany',
'languages': [
{'language': 'German'}
]
},
{
'country': ' Ireland',
'languages': [
{'language': 'English'},
{'language': 'Irish'}
]
}
]
I try to create a new list that 'language' contains 'eng'toLowwerCase(), but the error is Failed assertion: boolean expression must not be null
So pls help me, this is the full code:
void main() async {
List list = [
{'country': ' Wakanda', 'languages': null},
{
'country': 'USA',
'languages': [
{'language': 'English'}
]
},
{
'country': 'Germany',
'languages': [
{'language': 'German'}
]
},
{
'country': ' Ireland',
'languages': [
{'language': 'English'},
{'language': 'Irish'}
]
}
];
List filterList = List.from(list).where((e) {
return e['languages']?.any((l) => l['language'].toLowwerCase().contains('eng').toLowwerCase());
}).toList();
print(filterList);
}

Answer 1

The callback to Iterable.where must return a non-nullable bool type. Your callback potentially returns null if e['languages'] returns null:
return e['languages']?.any(
(l) => l['language'].toLowwerCase().contains('eng').toLowwerCase()
);
The way to fix it is to handle null. You can use x ?? y to provide a default value of y if x is null:
return e['languages']?.any(
(l) => l['language'].toLowwerCase().contains('eng').toLowwerCase()
) ?? false;
I'll also point out that:
toLowerCase() is misspelled.
List.from(list).where(...).toList() is redundant and could be just list.where(...).toList().

Answer 2

Try something like this
List filterList = List.from(list).where((e) {
// Avoid check null valúes
if (e['languages'] == null) {
return false;
}
return e['languages']?.any(
(l) => l['language'].toLowwerCase().contains('eng').toLowwerCase());
}).toList();
Also you can validate language child value

Answer 3

void main() async {
List list = [
{'country': ' Wakanda', 'languages': null},
{
'country': 'USA',
'languages': [
{'language': 'English'}
]
},
{
'country': 'Germany',
'languages': [
{'language': 'German'}
]
},
{
'country': ' Ireland',
'languages': [
{'language': 'English'},
{'language': 'Irish'}
]
}
];
List filterList = List.from(list).where((e) {
try{
return e['languages']?.any((l) =>
l['language'].toLowwerCase().contains('eng').toLowwerCase());
}).toList();
}
catch(e){
return [''];
}
print(filterList);
}