Error setting contentDetails for Youtube Live API v3

Error won't occur unless I put contentDetails into 4th line.

It seems that the error occurs when there are more than two in part section.
If I leave it just as :part => 'snippet',, everything works fine.
However I have to add contentDetails to gain information about duration of the videos on Youtube.

How can I archive it?

videos_controller.rb

@search_response = client.execute!(
  :api_method => youtube.search.list,
  :parameters => {
    :part => 'snippet, contentDetails',
    :q => 'cats',
    :maxResults => 20,
    :order => 'date',
    :pageToken => pageToken
  }
)

Error

ActionView::Template::Error (undefined method `prev_page_token' for nil:NilClass):
    1: 
    2: <% if !@search_response.prev_page_token.nil? %>