Better error message when context is missing
A common mistake when using proteus is to call .search instead of .find. In such case most of the time, the error is dues to the missing context. But the error message is not very clear as it says usually: "AttributeError: 'list' object has no attribute 'keys'" (because the domain is used as context).
So I propose to have more meaningful error message that will guide user to the right direction.