Method cache

rls/src/main/java/io/grpc/rls/LruCache.java:31–31

Populates a cache entry. If the cache entry for given key already exists, the value will be replaced to the new value. @return the previous value associated with key, otherwise null

(K key, V value)

   * @return the previous value associated with key, otherwise {@code null}
   */
  @Nullable
  V cache(K key, V value);

  /**