**LeetCode #102 - Binary Tree Level Order Traversal**\nGiven the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level). Ensure your solution is efficient and understands potential edge cases with tree structures.\n### Example 1: \n**Input:** root = [3,9,20,null,null,15,7] \n**Output:** [[3],[9,20],[15,7]] \n**Explanation:** Level order traversal of the binary tree is [[3],[9,20],[15,7]].\n### Example 2: \n**Input:** root = [1] \n**Output:** [[1]] \n**Explanation:** The tree only has one node.\n### Constraints: \n- The number of nodes in the tree is in the range [0, 10^4]. \n- -1000 <= Node.val <= 1000.