def filter(params)
      results = where(nil)
      params.each do |key, value|
        results = results.public_send(key, value) if value.present?
      end
      results
    end
def filter(params)
      results = where(nil)
      params.each do |key, value|
        results = results.public_send(key, value) if value.present?
      end
      results
    end
Iterates over params hash and
 applies non-empty values as filters
 @param params [Hash] filters list
 @return [ActiveRecord::Relation] filtered list