input: Write a function to convert all characters of a given string to lowercase. If the input string is empty, return an empty string. If the input string contains only non-alphabetic characters, return the string as-is.
  ensure convertToLowerCase("HELLO") == "hello"
  ensure convertToLowerCase("Hello World!") == "hello world!"
  ensure convertToLowerCase("") == ""
  ensure convertToLowerCase("12345") == "12345"
output: def convertToLowerCase(s):
      if s == "":
          return ""
      elif not any(c.isalpha() for c in s):
          return s
      else:
          return s.lower()