Thrift Dart generated code not working with dart 2.12.1

Generated dart code shows numerous errors when using with Dart 2.12.1 (in flutter).

Using tutorial.thrift and thrift generator 0.15.0

• Non-nullable instance field '_iprot' must be initialized. (Documentation)
• A value of type 'Object' can't be assigned to a variable of type 'int'. (Documentation)

Also for Flutter it's missing null-safety