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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 _validate_name(name):
 """Pre-flight ``Bucket`` name validation. :type name: str or :data:`NoneType` :param name: Proposed bucket name. :rtype: str or :data:`NoneType` :returns: ``name`` if valid. """

    if name is None:
        return

    # The first and las characters must be alphanumeric.
    if not all([name[0].isalnum(), name[-1].isalnum()]):
        raise ValueError("Bucket names must start and end with a number or letter.")
    return name