Metadata May Be Deleted When Blank

[emarinier]

Currently, the workflow may write a blank metadata entry to the Irida Next JSON (metadata_1 == ""). Irida will interpret this as instructions to delete an existing metadata entry with the same name. I don't think it's possible for this behaviour to come up with the locking functionality, but it may come up with other transformations.

We may wish to modify the workflow of the nf-iridanext plugin to control this behaviour better.