code: def unicode_to_hex(unicode_string):
      
      if unicode_string is None:
          return None
      acc = []
      for c in unicode_string:
          s = hex(ord(c)).replace("0x", "").upper()
          acc.append("U+" + ("0" * (4 - len(s))) + s)
      return u" ".join(acc)
docs: Return a string containing the Unicode hexadecimal codepoint
      of each Unicode character in the given Unicode string.
  
      Return ``None`` if ``unicode_string`` is ``None``.
  
      Example::
          a  => U+0061
          ab => U+0061 U+0062
  
      :param str unicode_string: the Unicode string to convert
      :rtype: (Unicode) str