Handle NullReferenceException in Foreign Key Classes (EF)

Hi all,
 
I have a small problem. The thing is, how to handle a NullReferenceException when accessing foreign key classes, in other words, check if the foreign key instance is null before calling / using it. For example:
 
Mammal.Human.FirstName - Where Human will be null. But I don't want to perform a null check for each foreign key class. For example: Mammal.Dog.Age (now Dog could be null).
 
Many thanks in advance!
Kind regards,