Please solve the programming task below using a self-contained code snippet in a markdown code block.

You are given an integer array nums. You must perform exactly one operation where you can replace one element nums[i] with nums[i] * nums[i]. 
Return the maximum possible subarray sum after exactly one operation. The subarray must be non-empty.
 
Please complete the following python code precisely:
```python
class Solution:
    def maxSumAfterOperation(self, nums: List[int]) -> int:
```