input: Write a function to detect the first vowel in a given string. If a vowel is found, return the vowel; otherwise, return an empty string. If the input string is empty, return an empty string.
  assert vowelCheck("Hello World")=='e'
  assert vowelCheck("Python")=='o'
  assert vowelCheck("BCDFG")==''
  assert vowelCheck("")==''
output: def vowelCheck(s):
      vowels = "aeiouAEIOU"
      for char in s:
          if char in vowels:
              return char
      return ""