use_if_null_to_convert_nulls_to_bools       
            
            Use if-null operators to convert nulls to bools.
This rule is available as of Dart 2.13.0.
Details
From Effective Dart:
Use if-null operators to convert nulls to bools.
BAD:
if (nullableBool == true) {
}
if (nullableBool != false) {
}
GOOD:
if (nullableBool ?? false) {
}
if (nullableBool ?? true) {
}
Usage
To enable the use_if_null_to_convert_nulls_to_bools rule,
add use_if_null_to_convert_nulls_to_bools under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - use_if_null_to_convert_nulls_to_bools