prefer_null_aware_method_calls    
            
            Prefer null aware method calls.
This rule is available as of Dart 2.14.0.
Details
Instead of checking nullability of a function/method f before calling it you
can use f?.call().
BAD:
if (f != null) f!();
GOOD:
f?.call();
Usage
To enable the prefer_null_aware_method_calls rule,
add prefer_null_aware_method_calls under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - prefer_null_aware_method_calls