You are given a sorted array of unique integers 'nums'. Your task is to find a pair of distinct elements in the array that are additive inverses of each other (their sum is exactly 0). Return the pair as a list [a, b] where a < b. If no such pair exists, return an empty list.
Explanation: The elements -2 and 2 are present in the array, and their sum is -2 + 2 = 0.
Explanation: There is no pair of distinct elements in the array that sum up to 0.