unnecessary_null_checks  
            
            Unnecessary null checks.
This rule is currently experimental and available as of Dart 2.12.0.
This rule has a quick fix available.
Details
DON’T apply a null check when a nullable value is accepted.
BAD:
f(int? i) {}
m() {
  int? j;
  f(j!);
}
GOOD:
f(int? i) {}
m() {
  int? j;
  f(j);
}
Usage
To enable the unnecessary_null_checks rule,
add unnecessary_null_checks under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - unnecessary_null_checks