private MColumnDescriptor createNewMColumnDescriptor(List<MFieldSchema> cols) {
    if (cols == null) {
      return null;
    }
    return new MColumnDescriptor(cols);
  }
Given a list of model field schemas, create a new model column descriptor.
@param cols the columns the column descriptor contains
@return a new column descriptor db-backed object
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java