The warning is not specific to that GEDCOM data file. If you start from the terminal, create a new tree and import the “sample.ged” file (in “example/gedcom”, bundled with Gramps), the symptom is the same. You just have to click through the various categories of the Navigator sidebar.
The warning appears to be because that importing a file does not make certain that there is an active record in each category. And does not set a Home Person. But most views need an active record to feed the Gramplets and a Home Person for most relationship features.
So the views complain if a Record is not active. This is a transitory condition that generally only affects brand new users. Because it is hard to NOT have active records if you’ve been using the software … even for a few minutes. So adding extra code to “setting active records in all categories by default” is probably of little interest to experienced developers.
However, the real issue is that the warning is not actionable. (I assume that there will be other circumstances that could cause this warning code to be used.) The text of the warning does not give enough of a clue about what caused the warning nor how to resolve an “empty handle”. It looks like there is damage to a particular object in the tree data. But it is just a missing selection in the GUI.