When you see values in Mixpanel as (No name) or (NULL) it means that an empty string was sent in as the value of that Property (as opposed to “undefined,” where the Property was not sent in at all).
NaN (Not a Number) means that a null value for numerical properties was returned when segmenting beneath a Funnel.
Remove (NULL) or NaN from reports
(NULL)/NaN values can be removed from reporting by typecasting the property to a boolean, and setting it equal to True.
Related Topic: What does an undefined property mean?