This issue came with the transition from JSON to SQLite for metadata storage:
The default values are -1 in the structs for the metadata (with the meaning of not set). In a SQLite table NULL has the meaning of not set, but when reading the data from the database NULL values are read as 0 and not -1.
This problem is very obvious when trying to export the metadata, as all fields are now considered set and written with the value 0.

Possible solutions:

• In SQL:
  1. Use a SQL-function like this:

  SELECT field_id, COALESCE(w_snr, -1.0) AS w_snr, COALESCE(b_psnr, -1.0) AS b_psnr FROM vits_metrics

  2. Use views
• In C++:
  1. Use isNull() to check values for NULL before setting the value
  2. Use a custom QVariant toInt()/toDouble() function that return -1 for NULL values

Not sure what the best-performing solution is, probably SQL views