[Bug] Can't unset repoDir parameter in aoptions

[MarcinKosinski]

If one would like to unset the repoDir parameter to be NULL as it is from the start (when the archivist package is loaded), it is impossible because when the second argument of aoptions is set to NULL then this function returns the argument instead of setting this parameter.

> library(archivist)
Welcome to archivist (version: 1.9.3.0).
> aoptions('repoDir')
NULL
> aoptions('repoDir', 'example')
[1] "example"
> aoptions('repoDir')
[1] "example"
> aoptions('repoDir', NULL)
[1] "example"

This functionality is crucial to unset repoDir when one would like to work with GitHub repo after he set Local repo and is using aread function that uses loadFromRepo function that checks global parameters. I recommend to add forceNULL parameter to the aoptions function. This is the cause of #175

[MarcinKosinski]

@pbiecek what do you think about such solution?

[pbiecek]

Will be better to find some other solution. Here the forceNULL is only to cover one special case. And NULL is not a real value it's lack of value.

Maybe we can use the value NA?
aoptions('repoDir', NA)
will work as expected and loadFromRepo can be prepared how to deal with NA.

Or use name like unset instead of forceNULL?

The second option is better since the name 'unset' corresponds to the expected behaviour of the function.