input: Write a function to determine if it is possible to print the Fibonacci series for a given number `n`. If `n` is less than or equal to 0, return `None`.
  def printFibonacciSeries(n): 
    
      if n <= 0: 
          return None
  
      # Taking 1st two fibonacci numbers as 0 and 1 
      f1 = 0
      f2 = 1
      print(f1, f2, end = " ") 
    
      for i in range(2, n): 
          next = f1 + f2 
          print(next, end = " ") 
    
          # update values 
          f1 = f2 
          f2 = next
  
  assert printFibonacciSeries(5)=='0 1 1 2 3 '
  assert printFibonacciSeries(0)==None
  assert printFibonacciSeries(-1)==None
  assert printFibonacciSeries(10)=='0 1 1 2 3 5 8 13 21 34 '
output: def printFibonacciSeries(n): 
      if n <= 0: 
          return None
  
      result = ""
      f1 = 0
      f2 = 1
      result += f"{f1} {f2} "
    
      for i in range(2, n): 
          next = f1 + f2 
          result += f"{next} "
    
          f1 = f2 
          f2 = next
  
      return result.strip()