AttributeError: 'NoneType' object has no attribute 'publickey_exp'

This error message means that you are trying to access the attribute "publickey_exp" of an object that is of type "NoneType". In other words, the object you are trying to access does not exist or is not assigned to a variable.

To fix this error, you need to make sure that the object you are trying to access actually exists and is assigned to a variable. If you are not sure where the error is coming from, you can use print statements or a debugger to help you track down the problem.