The object of returning the non-existing parameter is to return original input as the value, so if the input value is not parameter related, it will acting as string. I did not deeply review in this changes, but have you tested whether changing this makes string input became None in output json file?

Because of this line of code, None is transformed into the string 'Value was not specified' before saving the json. Does that answer the question?

See also here for more context.

I see your point, but we need to test if the proposed change impacts the hardcoded string in the METADATA_REF.

I recall there being a specific reason for this function to return a string. For instance, the template is designed to use string values that aren't present in the metadata files by default. For example, in /brkraw/lib/reference.py, the FMRI_META_REF has a key "CogAtlasID" where the value is a common string (URL) rather than a parameter. I'm concerned that the change you suggest might result in this value being labeled as "Value was not specified".

Ok, I get what you mean. In the commit above, I suggest a quick fix. It will only assign None to a parameter value when it is still a string within the function meta_check_express. I think it addresses your concern; let me know if not.

At a later time, it might be worth it to reconsider how the logic behind these checks is implemented.

Based on your suggestion, I'll focus on enhancing the logic BIDS converter for better readability and clarity over the next two weeks. I'll go ahead and merge this pull request. Thanks!