NoneType object has no attribute author

[cclauss]

Closes Sentry OL-WEB-88 which has been happening for 7 months and happened 17k times in the past 30 days and 1.1k times in the past 24 hours.

When get_version(page.key, page.revision) returns None, properly display the page instead of raising the exception AttributeError: 'NoneType' object has no attribute 'author'

Technical

Testing

Screenshot

Stakeholders

[mekarpeles]

I think even with this change there's still an issue:

[cclauss]

On the modified page openlibrary/templates/diff.html there are just three instances of author as an attribute.
Line 2 and 3 in the diff below. All three of those instances are short-circuited (not run) by the proposed change.

I cannot find the proposed change on testing dev-merged. Line two is not modified as proposed in this pull request.

➜  openlibrary git:(dev-merged) ✗ hostname
ol-dev1.us.archive.org
➜  openlibrary git:(dev-merged) ✗ git grep author openlibrary/templates/diff.html

openlibrary/templates/diff.html:    $elif a.type.key in ["/type/author"]:
openlibrary/templates/diff.html:        $if v.author:
openlibrary/templates/diff.html:            <span class="brown">$_('by') <a href="$v.author.key">$v.author.displayname</a> $datestr(v.created)</span>
openlibrary/templates/diff.html:                elif p == "authors":
openlibrary/templates/diff.html:                    label = "authors"
openlibrary/templates/diff.html:                    t = "/type/author"
openlibrary/templates/diff.html:                    ap = a.get_authors()
openlibrary/templates/diff.html:                    bp = b.get_authors()

[mekarpeles]

I think we may be trading errors -- I may have run this on ol-dev1 ol-mek. Let's merge and see if sentry confirms. Can't hurt?