For efficient lookup based on Class types as key,
a ClassValue should be used; however it requires
lazy association of values; this helper wraps
a plain HashMap but optimises lookups via the ClassValue.
N.B. there is a cost in memory and in terms of weak references,
so let's use this only where proven that a simple Map lookup
is otherwise too costly.
Fields inherited from interface org.hibernate.internal.util.collections.ReadOnlyMap