public List<ValueAttribute> getRequiresTrackedIsSetNonMandatoryAttributes() {
    ImmutableList.Builder<ValueAttribute> builder = ImmutableList.builder();
    for (ValueAttribute attribute : getSettableAttributes()) {
      if (attribute.requiresTrackIsSet()) {
        builder.add(attribute);
      }
    }
    return builder.build();
  }
Means object hashcode is cached at some point. Either lazily (on first access)
or eagerly (during construction).
@see #isUseLazyhash()
@see #isUsePrehashed()
value-processor/src/org/immutables/value/processor/meta/ValueType.java