google – What is the purpose of the recovery of user agent node, only retrieving the base URL on our site?

The user agent node-fetch/1.0 (+https://github.com/bitinn/node-fetch)
was looking for the base URL of the IP belonging to
251.232.178.107.gae.googleusercontent.com.

It is quite aggressive and comes from a large number of IP addresses. I wonder why the user agent only retrieves the base URL and that no other resource is loaded.

user agent

I would like to block it but I'm not sure it would be wise.