index: don't include nullid in len() I suspect the reason the nullid is in the index in the last position is that it lets index[i] for regular revision number, even when index was just a regular Python list. An alternative solution would have been to reserve revision number 0 for the null revision. I don't know why that wasn't done. Now that we have classes backing the index, we can easily make index[-1] get the nullid without having to put it last in the list and including it in the len(). This patch just hides the nullid -- it will still be accessible at index[len(index)]. I realize that this will be annoying when checking out across this commit for debugging (including bisection). Differential Revision: https://phab.mercurial-scm.org/D4022