overridden_fields 
            
            Don’t override fields.
This rule is available as of Dart 2.0.0.
Rule sets: recommended, flutter
Details
DON’T override fields.
Overriding fields is almost always done unintentionally. Regardless, it is a bad practice to do so.
BAD:
class Base {
  Object field = 'lorem';
  Object something = 'change';
}
class Bad1 extends Base {
  @override
  final field = 'ipsum'; // LINT
}
class Bad2 extends Base {
  @override
  Object something = 'done'; // LINT
}
GOOD:
class Base {
  Object field = 'lorem';
  Object something = 'change';
}
class Ok extends Base {
  Object newField; // OK
  final Object newFinal = 'ignore'; // OK
}
GOOD:
abstract class BaseLoggingHandler {
  Base transformer;
}
class LogPrintHandler implements BaseLoggingHandler {
  @override
  Derived transformer; // OK
}
Usage
To enable the overridden_fields rule,
add overridden_fields under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - overridden_fields