Add a new process "null"

In the development of the Antarctic Toothfish model, we have about 75 processes that implement the tagging by year and sub-area. For some years in some areas, there was no tagging. It would be helpful to allow checking of the config files to have a process that applies to every year in every sub-area, but some of those are set to “do nothing”, i.e., a process that is defined as

@process tag2017_south
type null

This allows the timesteps to be a complete list, but define that some of them do nothing as a null process.

It may be best that this has a switch to allow it to be recorded as a mortality process or not, depending on the user choice, i.e,

@process tag2017_south
type null
mortailty_process TRUE (or false as required)

Hopefully this is something that can be described in the description of your use case and the detailed definition of the tagging functionality.