don't show XML attributes if they ar eblank or nil

Hi, I'm creating a dynamic xml file using builder in Rails, which pulls
from several different related tables. Some of my nodes include
attributes, but some don't. I would like to find a way to leave out
those attributes that are blank.

My XML now:
<row type="bold" line="4">
<cell>Vermont </cell>
<cell>27%</cell>
</row>

<row type="" line="5">
<cell>Hawaii </cell>
<cell>100%</cell>
</row>

should look like this:
<row type="bold" line="4">
<cell>Vermont </cell>
<cell>27%</cell>
</row>

<row line="5">
<cell>Hawaii </cell>
<cell>100%</cell>
</row>

without the blank type="" attribute.

My .builder includes this:

@table.each do |r|
      xml.row(:line => r[0], :type=> r[1]) do
        r.each do |i|
          xml.cell(i, :column_id => '')
        end
      end
    end

I can make the value for :type => nil, but I still get the blank
attribute. I tried conditionals inside the node, but that didn't work.
Any ideas?

Thanks.