module Client
  class ClientException < Exception; end

  class Entity
    def foo(bar)
      raise ClientException unless bar

      "original #{bar}"
    end
  end
end

module ImprovedClient
  class Entity < Client::Entity
    def foo(bar)
      return unless bar

      original = super bar
      "decorated #{original}"
    rescue ClientException
      nil
    end
  end
end

# usage
entity = ImprovedClient::Entity.new
entity.foo 'baz' # => "decorated original baz"