Your idea

Is there an already existing rule for using (or not using) JSON null data type as content for a metadata field in BIDS ?

If not, I suggest we allow the usage of null if its meaning is specified for a given metadata field.

Here is an example from BEP028: we want to have the Command metadata to be REQUIRED to indicate which command line was used to generate some data. In the case where data is generated manually, null could be useful to indicate that no command was used. This is different from:

• no Command at all, which means we don't know the command ;
• "Command": "manual", which we could interpret as : the manual command was used.