public function header(Closure $closure = null)
    {
        if (!$closure) {
            return $this->header;
        }

        $this->header = $closure;

        return $this;
    }
public function header(Closure $closure = null)
    {
        if (!$closure) {
            return $this->header;
        }

        $this->header = $closure;

        return $this;
    }
public function header ( Closure $ closure = null ) { if ( ! $ closure ) { return $ this -> header ; } $ this -> header = $ closure ; return $ this ; }
Set grid header.

@param Closure|null $closure

@return $this|Closure
Set grid header .