ruby on rails - Only calling a method if a hash is populated -

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i have instance variable called 

@filtered_ratings = params[:ratings].keys

however, if params[:ratings] nil , #keys called on there error raised. if @filtered_ratings nil, want @filtered_ratings set empty array (or hash). there easy way of doing without code? thanks!

@filtered_ratings = params[:ratings].keys if params[:ratings].respond_to? :keys

edit:

 # if params[:ratings] nil return []  @filtered_ratings = params[:ratings].try(:keys) || []

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