Given a ParsedNode, add some fields that might be missing. Return a
        reference to the dict that refers to the given column, creating it if
        it doesn't yet exist.

def _get_node_column(cls, node, column_name):
        """Given a ParsedNode, add some fields that might be missing. Return a
        reference to the dict that refers to the given column, creating it if
        it doesn't yet exist.
        """
        if not hasattr(node, 'columns'):
            node.set('columns', {})

        if column_name in node.columns:
            column = node.columns[column_name]
        else:
            column = {'name': column_name, 'description': ''}
            node.columns[column_name] = column

        return column