GAP insurance is included in all NMAC leases, but it's kind of pointless with the LEAF since most of us drove off the lot with over $10,000 into the car (thanks mostly to the tax incentive) which covers the gap. GAP insurance covers the difference between the cash value of the car and what's owed on the car. If what's owed on the car is equal to or less than the insurance payout in the event of a totaled car, there's no worries for NMAC.
Scenario A: I lease a $30,000 car and only put $1,000 down. I crash the car a week later. The car has already depreciated $5,000. Insurance pays out $25,000 to the bank. Bank has $1,000. They will come to me for the other $4,000. GAP insurance covers this $4,000 difference.
Scenario B: I lease a $30,000 car and put $5,000 down. I crash the car a week later. The car has already depreciated $5,000. Insurance pays out $25,000 to the bank. Bank already has $5,000, so there's no problem.
GAP insurance is only required by banks (or NMAC in this case) when it's a low down payment lease. There's no such thing as a low down payment lease with the LEAF, since NMAC is guaranteed at least $7500 with ever lease.