input: Write a function to detect the vowel in a given string. The function should check each character in the input string and return the first vowel it encounters. If no vowel is found, the function should return None. If the input string is empty, the function should also 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("Rhythm")==None
  assert vowelCheck("Python")==None
  assert vowelCheck("")==None
  assert vowelCheck("aeiou")=='a'
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