input: Write a function to detect the vowel in a given string. If a vowel is found, return it; otherwise, return None. 
  
  def vowelCheck(inputString): 
      vowels = ['a','e','i','o','u','A','E','I','O','U'] 
      for x in inputString: 
          if x in vowels: 
              return x 
      return None
  
  assert vowelCheck("Hello World")=='e' 
  assert vowelCheck("This is a test")=='i' 
  assert vowelCheck("Python")==None 
  assert vowelCheck("AEIOU")=='A' 
  assert vowelCheck("")==None
output: def vowelCheck(inputString): 
      vowels = ['a','e','i','o','u','A','E','I','O','U'] 
      for x in inputString: 
          if x in vowels: 
              return x 
      return None