input: Write a function to edit the given Python code to prompt the user to enter the value of radius to calculate the area of a circle. If the radius entered is valid, the function should return the calculated area; otherwise, it should return None.
  assert calculate_circle_area(5) == 78.5
  assert calculate_circle_area(10) == 314.0
  assert calculate_circle_area(0) == 0.0
  assert calculate_circle_area(-5) == None
  assert calculate_circle_area(None) == None
output: def calculate_circle_area(radius):
      if radius is None or radius < 0:
          return None
      return 3.14 * radius * radius