19 days ago I asked you to have a look at the documentation for filters:
but your responses show me that you did not.
Also I think that you still circle around the idea that fields can be empty - which they cannot. If there is no data for a field, then the field cannot be found in the metadata. There is no table (or something similar) stored in the metadata that is reserved for a particular field.
So "MISSING" described it absolutely correctly: the field is not there, it is not emtpy. Taken seriously, a test for an empty string in a field that is not there should really produce an error (which thankfully does not happen)
As with many of your other posts you describe your problems very theoretically.
It would be much nicer if you could tell us the real situations, preferably with a screendump.
So: for which use-case do you need a test for the presence of data and the data type.
If you really need such operators but you
then I see a certain discrepancy as such operators are usually only used in codes, aren't they?