///
/// Returns next indexed key based on passed index
///
/// @access private
///
/// @param {Number} $index - index of breakpoint
///
/// @return {String}
///
/// @group Internal Functions
///
@function flint-next-index($index) {
	@return if(flint-is-number($index) and $index != 0, flint-steal-key($index + 1), false);
}