def content_for(*args,&block)
      if block
        helpers.content_for(*args,&block)
      else
        rawtext(helpers.content_for(*args))
        ''
      end
    end
def content_for(*args,&block)
      if block
        helpers.content_for(*args,&block)
      else
        rawtext(helpers.content_for(*args))
        ''
      end
    end
Rails content_for is output if and only if no block given