prefer_is_not_operator

Prefer is! operator.

When checking if an object is not of a specified type, it is preferable to use the 'is!' operator.

BAD:

if (!(foo is Foo)) {
  ...
}

GOOD:

if (foo is! Foo) {
  ...
}

To enable the prefer_is_not_operator rule, add prefer_is_not_operator under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - prefer_is_not_operator

If you're instead using the YAML map syntax to configure linter rules, add prefer_is_not_operator: true under linter > rules:

linter:
  rules:
    prefer_is_not_operator: true