I prefer to keep things simple.
I do not have any apples. My apple count is 0.
A vehicle does not have any Leadership. It's Leadership is 0.
Zero apples plus 1d6 is 1d6.
Zero Leadership plus 1d6 is 1d6.
It's not as bad as it sounds. Eldrad just spent one of his powers this turn to make your Walker BS/WS1, instead of exploding the head of your Warlord. Is that really such a bad trade?