static class ConcurrentHashMapV8.Node<K,V>
Key-value entry. This class is never exported out as a
user-mutable Map.Entry (i.e., one supporting setValue; see
MapEntry below), but can be used for read-only traversals used
in bulk tasks. Subclasses of Node with a negative hash field
are special, and contain null keys and values (but are never
exported). Otherwise, keys and vals are never null.