input: Write a python function to implement a queue with methods to check if it is empty, enqueue an item, dequeue an item, and get the size of the queue.
  assert q.isEmpty() == True
  q.enqueue(1)
  q.enqueue(2)
  assert q.isEmpty() == False
  assert q.size() == 2
  assert q.dequeue() == 1
  assert q.size() == 1
  assert q.dequeue() == 2
  assert q.isEmpty() == True
output: class Queue:
      def __init__(self):
          self.items = []
  
      def isEmpty(self):
          return len(self.items) == 0
  
      def enqueue(self, item):
          self.items.append(item)
  
      def dequeue(self):
          if not self.isEmpty():
              return self.items.pop(0)
          else:
              return None
  
      def size(self):
          return len(self.items)
  
  # Example usage:
  q = Queue()
  assert q.isEmpty() == True
  q.enqueue(1)
  q.enqueue(2)
  assert q.isEmpty() == False
  assert q.size() == 2
  assert q.dequeue() == 1
  assert q.size() == 1
  assert q.dequeue() == 2
  assert q.isEmpty() == True