Represent last_commit as Option<Commit>

[yihuang]

No description provided.

[liamsi]

At least a brief description that motivates the changes would be cool next time :-) (even if this a PR isn't to master). Something along the lines of:

Without these changes parsing an rpc response with an empty last_commit (e.g. on the first block), would err.

I've tested this locally... CI still doesn't run for PRs from forks :-/
Thanks again @yihuang!

[yihuang]

At least a brief description that motivates the changes would be cool next time :-) (even if this a PR isn't to master). Something along the lines of:

Without these changes parsing an rpc response with an empty last_commit (e.g. on the first block), would err.

I've tested this locally... CI still doesn't run for PRs from forks :-/
Thanks again @yihuang!

Thanks, next time, I'll write some description ;D