Exercise: last positive number

Write a function function lastPositive(nums) that returns the last positive number in the array nums. If the array has no positive numbers, the function returns null.

• lastPositive([3, -1, 5, -2]) → 5
• lastPositive([8, -3, -6]) → 8
• lastPositive([-1, 0, -5]) → null

Constraints: nums is an array of integers of length 0 to 20; 0 does not count as positive; for an empty array and for an array with no positive numbers the function returns null.

Do not add extra imports unless the task says so explicitly.