My solution using priority queue cannot pass test case like [[9,10],[4,9],[4,17]]

The result should be 2 but I returned 3, can anyone tell me how to fix this bug?

Thanks so much!

```
def minMeetingRooms(self, intervals):
"""
:type intervals: List[Interval]
:rtype: int
"""
if intervals is None or len(intervals) == 0:
return 0
intervals.sort(key = lambda x : x.start)
pq = []
pq.append(intervals[0].end)
for i in range(1, len(intervals)):
if intervals[i].start >= pq[-1]:
pq.pop()
pq.append(intervals[i].end)
return len(pq)
```