src/main/java/org/jboss/util/collection/ConcurrentSkipListMap.java
V getValidValue() {
            Object v = value;
            if (v == this || v == BASE_HEADER)
                return null;
            return (V)v;
        }
V getValidValue() {
            Object v = value;
            if (v == this || v == BASE_HEADER)
                return null;
            return (V)v;
        }
Return value if this node contains a valid key-value pair,
else null.
@return this node's value if it isn't a marker or header or
is deleted, else null.