[Urgent] fix generate model optional double type

[knottx]

The problem is when the json value doesn't have decimal sometimes.
For Example normal value.

{
    "some_value": 123.45
}

And then it works with before.

class Test {
    double? someValue;

    Test.fromJson(Map<String, dynamic> json) {
        someValue = json['some_value'];
    }
}

=======================================================

But sometimes when value doesn't have decimal like this in same attribute.

{
    "some_value": 123
}

It will be seen as an int, my solution should declare as num? first. then use toDouble()

class Test {
    double? someValue;

    Test.fromJson(Map<String, dynamic> json) {
        someValue = (json['some_value'] as num?)?.toDouble();
    }
}

[CpdnCristiano]

Thanks!
LGTM