'NoneType' object has no attribute 'next'

This error message is raised when you try to access the `next` attribute of a `NoneType` object. In Python, `None` is a special value that represents the absence of a value. It is often used to indicate a failure or error condition.

For example, if you have a variable that is supposed to contain a reference to an object, but that object does not exist, the variable will be set to `None`. If you then try to access an attribute or method of that variable, you will get an error like the one you described.

To fix this error, you need to make sure that the object you are trying to access actually exists. You should also check for `None` values before trying to access attributes or methods of objects. This can be done using an `if` statement or by using Python's built-in `getattr` function with a default value.

Here is an example of how to use `getattr` to safely access an attribute of an object:

my_object = None
my_attribute = getattr(my_object, 'my_attribute', default_value)

In this example, if `my_object` is `None`, the `getattr` function will return `default_value` instead of raising an error.