Second Largest Value

Write secondLargest(nums) that returns the second largest distinct value in nums.

• Distinct means repeated values count once. In [4, 9, 9, 7] the largest is 9 and the second largest is 7, not 9.
• If there is no second distinct value, return null. That covers an empty array, a one-item array, and an array where every item is equal.
• Numbers can be negative. They are all finite, so there is no Infinity or NaN.
• The array can be in any order. Don't change it.