1.1.4.4. nullability.NullablePassedToNonnull (ObjC)
Warns when a nullable pointer is passed to a pointer which has a _Nonnull type.

Examples:

typedef struct Dummy { int val; } Dummy;
Dummy *_Nullable returnsNullable();
void takesNonnull(Dummy *_Nonnull);

void test() {
  Dummy *p = returnsNullable();
  takesNonnull(p); // warn
}