If the key to be inserted into a HashMap is null and the table needs to be resized as part of the insertion then addEntry will try to recalculate the hash of a null key. This will fail with an NPE.
Reviewed-by: darcy
All of the hashing based Map implementations: HashMap, Hashtable, LinkedHashMap, WeakHashMap and ConcurrentHashMap are modified to use an enhanced hashing algorithm for string keys when the capacity of the hash table has ever grown beyond 512 entries. The enhanced hashing implementation uses the murmur3 hashing algorithm along with random hash seeds and index masks. These enhancements mitigate cases where colliding String hash values could result in a performance bottleneck.
Reviewed-by: alanb, forax, dl
