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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def hex_to_unichr(hex_string):
 """ Return the Unicode character with the given codepoint, given as an hexadecimal string. Return ``None`` if ``hex_string`` is ``None`` or is empty. Example:: "0061" => a "U+0061" => a :param str hex_string: the Unicode codepoint of the desired character :rtype: (Unicode) str """

    if (hex_string is None) or (len(hex_string) < 1):
        return None
    if hex_string.startswith("U+"):
        hex_string = hex_string[2:]
    return int_to_unichr(int(hex_string, base=16))