JsonArrayExtension extension
Creates a JsonArray from a Dart List.
Each non-null element is wrapped into a JsonValue, null stays null.
See also:
Example:
final a = [1, '2', null].json; // JsonArray
print(a[0]!.asNumber.intValue); // 1
print(a[1]!.asNumber.intValue); // 2
print(a[2]); // null