protected function _initColumn($column)
    {
        $defaults = [
            'type'  => 'string',
            'array' => false
        ];
        if (is_string($column)) {
            $column = ['type' => $column];
        } elseif (isset($column[0])) {
            $column['type'] = $column[0];
            unset($column[0]);
        }
        $column += $defaults;
        return $column + ['null' => false];
    }