JSON parsing / null pointer exception

[atoka93]

Thank you for the package.
I noticed the following issue in the crash reporting tool we use:

Describe the bug
Map for model As is sometimes null when parsing.

To Reproduce
Unsure how to reproduce, I saw the following crash log for an app:
geo.dart in new As.fromMap at line 245 within dart_ipify
geo.dart in new GeoModel.fromMap at line 56 within dart_ipify
geo.dart in new GeoModel.fromJson at line 65 within dart_ipify
dart_ipify_base.dart in Ipify.geo at line 133 within dart_ipify

Expected behavior
As or all of its fields should be set to null and it shouldn't throw an exception.

Smartphone (please complete the following information):

• Device: many different types
• OS: both iOS and Android
• Version: 1.1.1

Additional context
maybe ~5% of users experience it