Serialiser_Engine: Stop throwing error on System.DBNull

[Tom-Kingstone]

NOTE: Depends on

Issues addressed by this PR

Closes #3210

after many hours of searching, finally found out that System.DBNull should serialise as null, so we should stop throwing errors when trying to serialise it.

Test files

3210-DBNullCannotBeSerialised.zip Run through instructions made by myself in parent issue.

Changelog

Additional comments

[albinber]

@BHoMBot check compliance @bhombot check versioning

[bhombot-ci[bot]]

@albinber to confirm, the following actions are now queued: - check `code-compliance` - check `documentation-compliance` - check `project-compliance` - check `branch-compliance` - check `dataset-compliance` - check `copyright-compliance` - check `versioning`

[Tom-Kingstone]

@BHoMBot check core @BHoMBot check installer

[bhombot-ci[bot]]

@Tom-Kingstone to confirm, the following actions are now queued: - check `core` - check `installer` There are 24 requests in the queue ahead of you.

[FraserGreenroyd]

@BHoMBot check serialisation @BHoMBot check null-handling @BHoMBot check ready-to-merge

[bhombot-ci[bot]]

@FraserGreenroyd to confirm, the following actions are now queued: - check `serialisation` - check `null-handling` - check `ready-to-merge` There are 3 requests in the queue ahead of you.

[FraserGreenroyd]

@BHoMBot this is a DevOps instruction. I am requesting neutral checks on: unit-tests

[bhombot-ci[bot]]

@FraserGreenroyd I have provided neutral checks to the checks requested. These checks will need to be run properly to obtain full results.