code: @GwtIncompatible("To be supported")
    CacheBuilder<K, V> keyEquivalence(Equivalence<Object> equivalence) {
      checkState(keyEquivalence == null, "key equivalence was already set to %s", keyEquivalence);
      keyEquivalence = checkNotNull(equivalence);
      return this;
    }
docs: Sets a custom {@code Equivalence} strategy for comparing keys.
  
  <p>By default, the cache uses {@link Equivalence#identity} to determine key equality when
  {@link #weakKeys} is specified, and {@link Equivalence#equals()} otherwise.