Reports fields, parameters and return values of methods which do not have a nullability annotation, like @NotNull or @Nullable.
Quick fixes are presented to add one of the annotations to the elements with a problem.
When your project uses 'default' annotations like @ParamsAreNonnulByDefault by means of JSR305' javax.annotation.meta.TypeQualifierDefault, a quick fix will be presented to apply the annotation to the current package by adding the annotation to the package-info.java. If a package-info.java doesn't exist yet it will be created automatically.
Only annotations registered with IntelliJ will be suggested in the quick fixes. Go to Preferences | Build | Compiler | Configure annotations ... to register your own.
: Any nullability annotation can be used, like JSR-305, JetBrains' or your own as long as you configure them in IDEA.