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

Given an integer array arr and an integer k, modify the array by repeating it k times.
For example, if arr = [1, 2] and k = 3 then the modified array will be [1, 2, 1, 2, 1, 2].
Return the maximum sub-array sum in the modified array. Note that the length of the sub-array can be 0 and its sum in that case is 0.
As the answer can be very large, return the answer modulo 109 + 7.
 
Please complete the following python code precisely:
```python
class Solution:
    def kConcatenationMaxSum(self, arr: List[int], k: int) -> int:
```