void initNullabilitySupertype(ExecutableElement accessor) {
    if (nullabilityInSupertype == null && !isPrimitive() && !isNullable()) {
      nullabilityInSupertype = isAccessorNullableAccessor(accessor);
    }
  }
Init (or override) internal attributes specific to JavaBeans
value-processor/src/org/immutables/value/processor/meta/ValueAttribute.java