ImmutableList<ValueAttribute> collect() {
          addUnique(getMarshaledAttributes());
          addUnique(getUnmarshaledAttributes());
          return ImmutableList.copyOf(byNames.values());
        }
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