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