single import csv breaks on dupe legacyid if some but not all ids given

[whatisgalen]

If you import data via Import Single CSV module and provide a uuid value for some, but not all of a column selected as "use as id", you can get an error complaining about duplicate legacyid values:

2024-08-20 19:37:23,449 arches.app.etl_modules.save ERROR    duplicate key value violates unique constraint "resource_instances_legacyid_key"
DETAIL:  Key (legacyid)=() already exists.
CONTEXT:  SQL statement "INSERT INTO resource_instances(resourceinstanceid, graphid, legacyid, createdtime)
                                 VALUES (instance_id, graph_id, legacy_id, now())"
 PL/pgSQL function __arches_staging_to_tile(uuid) line 39 at SQL statement

On the frontend, the load operation will fail but the error/alert banner says "Please contact your system administrator" without any specific errors mentioned.