Related to the fix released for #2606, running pylint over a local subclass of ColumnBase raises the following:

Method '__iter__' is abstract in class 'ColumnBase' but is not overridden (abstract-method)

Raising NotimplementedError implies that a concrete class is meant to implement this abstract method. According to the python docs, if __iter__ is never to be implemented on a subclass of ColumnBase, then it should be set to None