Leetcode: Missing Ranges

Given a sorted integer array where the range of elements are [lower, upper] inclusive, return its missing ranges.

For example, given [0, 1, 3, 50, 75], lower = 0 and upper = 99, return ["2", "4->49", "51->74", "76->99"].

Understand the problem:
The problem itself is not hard at all. The key is to handle several corner cases. e.g. 
 -- If the array is empty, the missing ranges should be from lower to upper, inclusive. 
 -- For the leading missing range, e.g. -2 , [-1], -1. The output should be "-2". Note that the lower bound is inclusive. 
 -- For the trailing missing range, e.g. -2, [-2], 1, the output should be "-1->1". The upper bound is inclusive as well. 

Code (Java):

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public class Solution {     public List<String> findMissingRanges(int[] nums, int lower, int upper) {         List<String> result = new ArrayList<String>();         if (nums == null || nums.length == 0) {             outputToResult(lower, upper, result);             return result;         }                   // leading missing range         if (nums[0] - lower > 0) {             outputToResult(lower, nums[0] - 1, result);         }                   for (int i = 1; i < nums.length; i++) {             if (nums[i] - nums[i - 1] > 1) {                 outputToResult(nums[i - 1] + 1, nums[i] - 1, result);             }         }                   // trailing missage ranges         if (upper - nums[nums.length - 1] > 0) {             outputToResult(nums[nums.length - 1] + 1, upper, result);         }                   return result;     }           private void outputToResult(int start, int end, List<String> result) {         StringBuffer sb = new StringBuffer();         if (start == end) {             sb.append(start);         } else {             sb.append(start + "->" + end);         }                   result.add(sb.toString());     } }