code: public static Set<String> getKeyPropertyNames(EntityType entityType) {
          Set<String> keyPropertyNames = entityType.getKey().getPropertyRefs().stream()
                  .map(PropertyRef::getPath).collect(Collectors.toSet());
          return keyPropertyNames;
      }
docs: Gets the names of the properties that are part of the key of an entity type.
  
  @param entityType The entity type.
  @return A {@code Set} containing the names of the key properties of the entity type.