class RuboCop::Cop::Style::FileNull

def on_new_investigation
  return unless (ast = processed_source.ast)
  @contain_dev_null_string_in_file = ast.each_descendant(:str).any? do |str|
    content = str.str_content
    valid_string?(content) && content.downcase == '/dev/null' # rubocop:disable Style/FileNull
  end
end