input: Write a function to generate a multiplication table with numbers in a given range using start and end parameters. If the start and end parameters are provided, the function should print the multiplication table for numbers within that range. If the range is not provided, the function should return None.
  assert multiplication_table(5, 10)
  assert multiplication_table(1, 3)
  assert multiplication_table(0, 0)
  assert multiplication_table() == None
output: def multiplication_table(start=None, end=None):
      if start is None or end is None:
          return None
      for i in range(start, end + 1):
          for j in range(1, 11):
              print(f"{i} x {j} = {i * j}")
          print()