public static String prependNotNullCatToDbName(String catalogName, String dbName) {
    assert catalogName != null;
    return prependCatalogToDbName(catalogName, dbName, null);
  }
Given a catalog name and database name, cram them together into one string.  These can be
parsed apart again via {@link #parseDbName(String, Configuration)}.
@param catalogName catalog name.  This cannot be null.  If this might be null use
                   {@link #prependCatalogToDbName(String, String, Configuration)} instead.
@param dbName database name.
@return one string that contains both.
standalone-metastore/metastore-common/src/main/java/org/apache/hadoop/hive/metastore/utils/MetaStoreUtils.java