Flutter check if a class have a contain a key - flutter

Question

I'm new to flutter,
My project work when I don't use my class but I want to use class so I change my project for use that and I have some problems.
In my code how to check if the parameter that I use in my function as KeyReference exist in my class ?
And how to use my parameter keyReference for search in my list of user ?
This is my class :
class User{
int type;
String name;
num index;
User({
this.type,
this.name,
this.index,
});
User.fromJson(Map<String, dynamic> map){
type = map['type'];
distance = map['name'];
hausse = map['index'];
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = Map<String, dynamic>();
data['type'] = this.type;
data['distance'] = this.name;
data['hausse'] = this.index;
}
And this is my function :
static List<User> getListItemsEquality(var value, String keyReference, List<User> items)
{
//**************** Error ****************//
if(items == null)
{
throw MyException.noData();
}
items.forEach((item) {
// =================================================================================
// I have an error on this The method 'containsKey' isn't defined for the type 'User'.
//=================================================================================
if(!item.containsKey(keyReference)){
throw MyException.parameterNotExist();
}
});
//**************** Script ****************//
// =================================================================================
// The getter 'keyReference' isn't defined for the type 'Charge'.
//=================================================================================
return items.where((c) => (c.keyReference == value)).toList();
}