scala/scala — pull request #1839 by JamesIry (2013-01-04 00:04:34+00:00)
Title: SI-6908 Makes FlatHashTable as well as derived classes support nulls

This change adds a null sentinel object which is used to indicate that a null
value has been inserted in FlatHashTable. It also makes a strong distinction
between logical elements of the Set vs entries in the hash table. Changes
are made to mutable.HashSet and ParHashSet accordingly.

review by @adriaanm