Arr["where"] = function (func?: Predicate<T>): ArrayX<T> {
     var arr = [];
     var self = (this as any[]);
     for (var i = 0; i < self.length; i++)
         if (isNil(func) || func(self[i], i) === true)
             arr.push(self[i]);
     return new ArrayX<T>(...arr);
 }

            Arr["last"] = function (func?: Predicate<T>): T {
                var self = (this as X.Array<T>);

                var lastOrDefault = self.lastOrDefault(func);
                if (isNil(lastOrDefault))
                    throw new Error("Last item not found");
                else
                    return lastOrDefault;
            }

 const hasValue = (x: any) => !isNil(x);