private static boolean isSystemNamespace(String[] namespace) {
    return namespace.length == 1 && namespace[0].equalsIgnoreCase("system");
  }
List the functions in a namespace from the catalog.

<p>If there are no functions in the namespace, implementations should return an empty array.

@param namespace a multi-part namespace
@return an array of Identifiers for functions
@throws NoSuchNamespaceException If the namespace does not exist (optional).
amoro-format-mixed/amoro-mixed-spark/v3.5/amoro-mixed-spark-3.5/src/main/java/org/apache/amoro/spark/SparkUnifiedSessionCatalog.java