AssimpContext.ImportFileFromStream formatHint?

As I have asynchronous framework loading data transparent from server/local I always would like to handle data as byte-array. Unfortunatly I found no detailed information about AssimpContext.ImportFileFromStream about the formatHint parameter. Furthermore, aiImportFileFromMemory() from the native code allows so send an empty string to find out format by itself but the managed level does not permit it.
Can you tell me what I have to pass to the this argument?

Start by reading the managed AssimpContext.ImportFileFromStream API and compare its formatHint handling with native aiImportFileFromMemory(). Confirm what values the managed method accepts and whether an empty hint is rejected. Done means the accepted behavior is documented or aligned with the native API, with coverage for format detection.

Written by the indexing model from the issue text.