': Return the default unit for value, or None.
= INPUT VARIABLES
- value   The value or list of values that need units.
= RETURN VALUE
- Returns the default units to use for value.'

@staticmethod
def default_units(value, axis):

    frame = None
    if (iterable(value) and (not isinstance(value, six.string_types))):
        return EpochConverter.default_units(value[0], axis)
    else:
        frame = value.frame()
    return frame
