prefer_asserts_in_initializer_lists    
            
            Prefer putting asserts in initializer lists.
This rule is available as of Dart 2.0.0.
Details
DO put asserts in initializer lists.
BAD:
class A {
  A(int a) {
    assert(a != 0);
  }
}
GOOD:
class A {
  A(int a) : assert(a != 0);
}
Usage
To enable the prefer_asserts_in_initializer_lists rule,
add prefer_asserts_in_initializer_lists under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - prefer_asserts_in_initializer_lists