Don't show div surrounding a yield if nothing calls it

I have this snippet in a layout:

    <div class="yui-g" style="min-width: 760px">    
      <!-- top row -->  
        <%= yield :top_row %>
    </div>

If nothing calls content_for :top_row then i'm left with a styled, empty rectangle on the page. The right thing to do would be restyle the layout (and the whole site tbh) but that's not an option right now (le开发者_如何学Gogacy debt and more pressing requirements). Is there a way to wrap the div in some code that checks if the yield is actually yielding to anything, and to not render it if so?

cheers, max

EDIT - this is a rails 2.2.2 project btw.

EDIT 2

@arnep suggested the following, which works:

<% content = yield :top_row %>
<% unless content.blank? %>
  <div class="yui-g" style="min-width: 760px">   
    <%= content %>
  </div>
<% end %>

What i'd like to do next is to wrap that up in a helper which i can use like so:

<% yield_if(:top_row) do |content| %>
  <div class="yui-g" style="min-width: 760px">   
      <%= content %>
  </div>
<% end %>    

I'm struggling with that helper though, since it involves yielding in the block passed to the method AND yielding to the content in :top_row. Here's what i tried, which doesn't work - it renders the whole page into the returned string. I think i've got it backwards somehow.

def yield_if(content_name, &block)
  content = yield content_name 
  if content.blank?  
    ""
  else
    yield content 
  end
end 

Yep, there is a content_for? helper just for that of checking.

I looked at the 2.2.2 content_for and it uses instant_variable_set for this. May be you can use instance_variable_defined? to query for your :top_row content.

Another idea could be to assign the content to a variable <% content = yield(:top_row) %> and then use content.present? to circumvent an empty div.

Since you've no access to content_for?, the only way to go through this seems to use javascript and remove the div if it's empty.