Velocity is interpreting int i = 0 as boolean false

If I check var int i = 0 for existing I get wrong result:

#if($i)
  <output>$i</output>
#end

results in:

i not defined --> no output
i = 0         --> no output
i = 1         --> <output>1</output>

How can I tell velocity to consider value 0 as defined?

i not defined --> no output
i = 0         --> <output>0</output>
i = 1         --> <output>1</output>