The public API only returns UUIDs for the nodes it finds. This is a generic policy in the public API.
The FINGERPRINT keyword in the query language currently expects a DBID - this can not be obtained via the public API - particularly when executing a query.
As a developer will only be able to get the UUID the fingerprint keyword should accept this.
FINGERPRINT is currently unusable via the public API.
Scope is limited to SOLR 6 and this keyword in the query language.
Can not affect any existing tests as this is a new keyword in the QL.
There is a current fix with unit tests waiting final end-to-end verification using the public API.