Armor Values

[TankerACG20]

Hi all,
  Arnor Value 0. 
  While playing 1940 Fall of France,  my opponent attacked one of my armor units with a machine gun.
The armor unit had an Armor Value of 0. He argued that Armor Value 0 means no armor at all. 
I argued an armor value 0 indicates the vehicle's armor cannot defend adainst an anti-tank attack.
The vehicle's armor can defend against machine gun fire. In the end, I let him conduct his machine gun,
which missed the target.
  What is the correct rule to use in this situation?
  Please forgive me if this question is posted elsewhere.
Dave