input: Write a function to calculate the distance between two points on a two-dimensional plane given their coordinates. If either of the coordinates is None, the function should return None.
  assert distanceBetweenPoints(3, 4, -9, -2)==15.62
  assert distanceBetweenPoints(0, 0, 0, 0)==0
  assert distanceBetweenPoints(-4, -7, 1, 9)==15.62
  assert distanceBetweenPoints(None, 4, -9, -2)==None
  assert distanceBetweenPoints(3, 4, None, -2)==None
output: def distanceBetweenPoints(x1, y1, x2, y2):
      if x1 is None or y1 is None or x2 is None or y2 is None:
          return None
      return ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** 0.5