def CalculateOSNames(os_name, os_variants):
  """Calculates all the names an OS can be called, according to its variants.

  @type os_name: string
  @param os_name: base name of the os
  @type os_variants: list or None
  @param os_variants: list of supported variants
  @rtype: list
  @return: list of valid names

  """
  if os_variants:
    return ["%s+%s" % (os_name, v) for v in os_variants]
  else:
    return [os_name]