ModifyingCollectionWithItself

Invoking a collection method with the same collection as the argument is likely incorrect.

• collection.addAll(collection) may cause an infinite loop, duplicate the elements, or do nothing, depending on the type of Collection and implementation class.
• collection.retainAll(collection) is a no-op.
• collection.removeAll(collection) is the same as collection.clear().
• collection.containsAll(collection) is always true.