------
## 最终结论
```python
def common_element(list1, list2):
    for element in list1:
        if element in list2:
            return True
    return None

# Test cases
assert common_element([1,2,3,4,5], [5,6,7,8,9])==True
assert common_element([1,2,3,4,5], [6,7,8,9])==None
assert common_element(['a','b','c'], ['d','b','e'])==True
```