input: Write a function to detect the vowel in a given string. If there is a vowel in the string, return the first occurrence of the vowel. If there is no vowel in the string, 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
  assert vowelCheck("Hello World")=='e'
  assert vowelCheck("Fly")==None
  assert vowelCheck("PYTHON")==None
  assert vowelCheck("Alpha")=='A'
  assert vowelCheck("Enterprise")=='e'
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