No XML rendered in this example, why not?

Rails
1

I know I’m calling the controller correctly, I get

XML Parsing Error: no element found
.xml;example
Line Number 1, Column 1:

def example
xml = Builder::XmlMarkup.new(:indent=>2)
xml.instruct!
xml.person
return xml

respond_to do |format|
  format.html # index.rhtml
  format.xml  { render :xml => xml }
end

end