input: Write a function to search for a given string in a list of strings and return whether there is a match or not. The function should use regular expressions for the search. If the input string is empty, it should return "String doesn't match".
  
  assert search_string(["First", "Second", "Third"], "First") == "String matches"
  assert search_string(["First", "Second", "Third"], "Second") == "String matches"
  assert search_string(["First", "Second", "Third"], "Fourth") == "String doesn't match"
  assert search_string(["First", "Second", "Third"], "") == "String doesn't match"
  assert search_string([], "First") == "String doesn't match"
output: import re
  
  def search_string(lst, s):
      if not s:
          return "String doesn't match"
      for item in lst:
          if re.search(s, item):
              return "String matches"
      return "String doesn't match"