AttributeError: NoneType object has no attribute
The error "AttributeError: 'NoneType' object has no attribute..." probably means that you attempted to retrieve an object (such as a person, or family) by using its internal handle, but the database can't find it. Likely, the object is still there, but the internal database references have gotten corrupted.
To fix, first, make a Gramps XML backup.
Then, you need to run the menu -> Tools -> Family Tree Repair and run the tools:
1) Check and Repair Database 2) Rebuild Reference Maps 3) Rebuild Secondary Indices
in that order.
If you still get the error after running the repair tools, then you should try creating a new family tree, and importing your backup. If still errors, try running the above tools on the re-imported tree.
If you still have issues, you may need to go back to an older backup.