Cosmo SDK Polling app

As described in the tutorial:
https://tutorials.cosmos.network/voter/#x-voter-keeper-vote-go

Do i have to create a new file for the file mentioned in the tutorial?
x/voter/keeper/vote.go

Why it only contains one line?
key := []byte(types.VotePrefix + vote.PollID + “-” + string(vote.Creator))

After i add the file vote.go , the Polling app cannot be built.

Sorry, have to run the command to create vote.go
starport type vote pollID value