def romanise(number):
    """Return the roman numeral for a number.

    Note that this only works for number in interval range [0, 12] since at
    the moment we only use it on realtime earthquake to conver MMI value.

    :param number: The number that will be romanised
    :type number: float

    :return Roman numeral equivalent of the value
    :rtype: str
    """
    if number is None:
        return ''

    roman_list = ['0', 'I', 'II', 'III', 'IV', 'V', 'VI', 'VII', 'VIII',
                  'IX', 'X', 'XI', 'XII']
    try:
        roman = roman_list[int(number)]
    except ValueError:
        return None
    return roman