This driver does, as the name implies, nothing. It's mainly used for debugging purposes. As LCD4Linux insists on a display driver, you can use this one if you don't really need one.
Display <name> {
Driver 'NULL'
Size <string>
}
| Driver | 'NULL' |
| Size | The size of the (virtual) display, specified as '<columns>x<rows>' (e.g. '20×4') |