@Override
  public Map<String, String> loadNamespaceMetadata(String[] namespace)
      throws NoSuchNamespaceException {
    if (namespaceExists(namespace)) {
      return ImmutableMap.of();
    }
    throw new NoSuchNamespaceException(namespace);
  }
Unified catalog implement for spark engine.
amoro-format-mixed/amoro-mixed-spark/amoro-mixed-spark-3-common/src/main/java/org/apache/amoro/spark/SparkUnifiedCatalogBase.java