Error in validObject(.Object) : invalid class “prism” object: invalid key

[faenee]

Hello,
I wonder if there is no maglinant cells in my scRNA-seq data, how should I set the key arguments to be NULL.
I see the HELP DOCUMENT "key: The character string that correponds to malignant cells in cell.type.labels. =_NA_value if is set to NULL." And I do it as it says, but it doesn't work.

Looking forward to your reply.
Thanks a lot.