public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) {
        return map().computeIfAbsent(key, mappingFunction);
    }
Calls computeIfAbsent on underlying map, useful when cache is meant to behave as a pull-thru.
@param key tke key
@param mappingFunction the function called if key does not associate to a value
@return the value associated to the key
standalone-metastore/metastore-common/src/main/java/org/apache/hadoop/hive/metastore/properties/SoftCache.java