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

Given an array nums of n integers, return an array of all the unique quadruplets [nums[a], nums[b], nums[c], nums[d]] such that:

0 <= a, b, c, d < n
a, b, c, and d are distinct.
nums[a] + nums[b] + nums[c] + nums[d] == target

You may return the answer in any order.
 
Please complete the following python code precisely:
```python
class Solution:
    def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
```