NoMethodError in Lag#index

Showing /home/app/webapp/app/views/lag/index.rss.builder where line #46 raised:

undefined method `formatted_start_url' for #<#<Class:0x007feb3dc83450>:0x007feb40352e28>
Extracted source (around line #46):
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xml.pubDate article.created_on.to_s(:rfc822)
xml.link formatted_start_url(article, :html)
# xml.guid formatted_lag_index_url(article)
# xml.link formatted_lag_index_url(article, :rss)

Rails.root: /home/app/webapp

Application Trace | Framework Trace | Full Trace

Request

Parameters:

{"lag"=>"fu",
 "id"=>"10",
 "format"=>"rss"}

Response

Headers:

None