Question

For example if you pass a car into a sub that makes use of a car who should be checking for null references?

Should I even bother wrapping this code in the below if statement? It seems quite redundant, obviously I could have given a better example because I can’t catch the exception and handle it in any way.

Or should I just let the exception bubble up to the caller?

For example:

Public Sub CarService(ByVal car As ICar)
    If car IsNot Nothing Then
        'do logic here 
    Else : Throw New ArgumentNullException
    End If
End Sub

Answer 1

Throwing a NullReferenceException yourself is actually pointless. As this is

1. the same exception that the CLR would raise (at least when you
   access the same reference that you manually check for null) and
2. is discouraged anyway. See Remarks
   here. For a related discussion see Is it necessary to throw a NullReferenceException from an extension method?.

You should however, arguably at least for the public API surface, check for null references and throw an ArgumentNullException.

Public Sub CarService(ByVal car As ICar)
    If car Is Nothing Then
        Throw New ArgumentNullException("car")
    End If
    ' do logic here
End Sub

Or look into Code Contracts.