prefer_null_aware_operators   
            
            Prefer using null aware operators.
This rule is available as of Dart 2.2.0.
Rule sets: recommended, flutter
This rule has a quick fix available.
Details
PREFER using null aware operators instead of null checks in conditional expressions.
BAD:
v = a == null ? null : a.b;
GOOD:
v = a?.b;
Usage
To enable the prefer_null_aware_operators rule,
add prefer_null_aware_operators under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - prefer_null_aware_operators