public V putIfAbsent(K key, V value) {
        return map().putIfAbsent(key, value);
    }
Calls putIfAbsent on underlying map, useful when cache is meant to behave as a pull-thru.
@param key tke key
@param value the value
@return the value associated to the key
standalone-metastore/metastore-common/src/main/java/org/apache/hadoop/hive/metastore/properties/SoftCache.java