Prepare args to be used by a sub-index

        Parameters
        ----------
        args: list
            The while list of arguments passed to add, check_uniqueness, get_filtered_keys...
        transform: bool
            If ``True``, the last entry in `args`, ie the value, will be transformed.
            Else it will be kept as is.

def prepare_args(self, args, transform=True):
        """Prepare args to be used by a sub-index

        Parameters
        ----------
        args: list
            The while list of arguments passed to add, check_uniqueness, get_filtered_keys...
        transform: bool
            If ``True``, the last entry in `args`, ie the value, will be transformed.
            Else it will be kept as is.

        """
        updated_args = list(args)
        if transform:
            updated_args[-1] = self.transform_value(updated_args[-1])
        if self.key:
            updated_args.insert(-1, self.key)

        return updated_args