input: Write a function to detect the vowel in a given string. If a vowel is found, return the vowel. If no vowel is found, 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("Python")=='o'
  assert vowelCheck("Rhythm")==None
  assert vowelCheck("AEIOU")=='A'
  assert vowelCheck("bcdfg")==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