input: Write a function to remove all consecutive duplicates from a given string and return the resultant string. If the input string is empty, return an empty string.
  assert remove_duplicates("AAABBCCCD")=="ABCD"
  assert remove_duplicates("A")=="A"
  assert remove_duplicates("AB")=="AB"
  assert remove_duplicates("AABBCC")=="ABC"
  assert remove_duplicates("")==""
output: def remove_duplicates(s):
      if not s:
          return ""
      result = [s[0]]
      for char in s[1:]:
          if char != result[-1]:
              result.append(char)
      return ''.join(result)