Code review comment for lp:~lifeless/python-oops-tools/bug-879309

This looks good.

The only comment I have is an ignorable bikeshed: I had to read the
comment explaining the reason for using an empty string page ID a couple
of times before I understood it. Maybe replacing the colons with words
would help:

    # Missing topics are '' which will group all such reports together
    # in some ways, but thats tolerable vs something (near) unique like
    # a url which prevents aggregation.