[Internal] [Bug] Mistake in metadata validation not allowing valid strings

[jessicarowell]

Need to modify populate_fields() function assert statement to allow valid strings and not only "" or "Not Provided"

Run environment (container, cloud service, HPC, platform, etc.)
Any

Command to replicate the error:
nextflow run main.nf -profile test,singularity --species bacteria --output_dir test_bact --submission_config ~/02.scratch/submission_config.yaml --bakta_db_path /scicomp/reference/bakta/db

Any Additional Context or Information?
This mistake got missed with viral test data because all the terms_2_replace were missing. In bacteria test data, isolation_source = "Clinical," which is a valid string that was getting caught in the incorrect assert statement.

[jessicarowell]

This is completed and will be closed with the next PR

[jessicarowell]

Fixed on ick4-dev-patch