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

You are given an integer array nums and an integer k. Append k unique positive integers that do not appear in nums to nums such that the resulting total sum is minimum.
Return the sum of the k integers appended to nums.
 
Please complete the following python code precisely:
```python
class Solution:
    def minimalKSum(self, nums: List[int], k: int) -> int:
```