Why not set builder->next_phase_at=InvalidTransactionId in SnapBuildRestore function?

Hi, guys:

In PG14 or higher version, I notice that SnapBuildRestore don't set builder->next_phase_at=InvalidTransactionId .

But in SnapBuildSerialize function, the assert check this condition.

Assert(builder->next_phase_at == InvalidTransactionId);

I'd like to know is this right?

Thanks.