NullableOnContainingClass - Error Prone

The correct syntax to apply a TYPE_USE annotation to an inner class is A.@Nullable B.

For a TYPE_USE @Nullable annotation, @Nullable A.B is legal Java if B is a non-static inner class:

java

class A {
  @Target(TYPE_USE)
  @interface Nullable {}

  class B {}
  static class C {}

  void test(A.@Nullable B x) {} // B is annotated ('A' is the enclosing instance type)
  void test(A.@Nullable C x) {} // C is annotated ('A' is a 'scoping construct' here)
}

java

  void test(@Nullable A.B x) {} // compiles, but likely incorrect: annotates the enclosing instance type 'A', which can never be null
  void test(@Nullable A.C x) {} // compile error: 'A' cannot be annotated

However, for @Nullable (and @NonNull, and friends), annotating the outer class is meaningless. The reference to the outer class (A.this) can never be null, so any nullability annotations are redundant.