Thanks for the heads up. I'll investigate.

On a quick note I think replacing above line with the following should do the trick:

output['best-image-uri'] = best_image_uri or ''

Thanks @ibnesayeed, but the JavaScript should be less brittle. Only fixing the problem in /services/memento.py ignores the machine endpoints in /services/product.py.

Well, it has to do with how Python converts None to string. While None is a falsy object in boolean context, when converted to string it does not return a falsy string (i.e. an empty sting).

>>> str(None)
'None'

This means we need to be careful where we not want that to happen. One way to fix this issue for various different places where it might be used is to change the default value of max_score_image from None to an empty string at the following line.

The problem is actually larger that that. This is part of it, but there is a larger issue with the image selection code. I'll give details soon.

A similar issue often surfaces in JS as well where falsy null or undefined will be converted to strings as a word, not an empty string. I usually use a similar logical operator trick to canonicalize such variables in string context as it can be seen in the Reconstructive repo.

rels.first && rels.first.href || ''

The above JS line can be interpreted as:

(rels.first && rels.first.href) || ''

The way logical operators are executed is if there is an AND between two statements, the value of the first one will be returned if it is falsy, otherwise the value of the second will be returned instead. And if there is an OR then the first one will be returned if it is truthy, otherwise the value of the second one will be returned instead.

So, in the above example it means check the value of rels.first.href if and only if rels.first is not null (to avoid an exception like cannot read property 'href' of null object) and return the value of rels.first.href if it is not falsy. Otherwise the statement in parenthesis returns falsy (due to the first one or the second) then return the value after the OR operator, which is an empty string.

The MementoEmbed code will be modified to provide a default image if none is found.