NRF GET nf-instances handles optional parameters as mandatory

I noticed a behaviour in the NRF nnrf-nfm/v1/nf-instances that does not seem correct to me. When I call

curl ''   -H 'accept: application/json'

I get a 400 Bad Request with the following body:

{"title":"Invalid Parameter","status":400,"detail":"strconv.Atoi: parsing \"\": invalid syntax"}

When I add ?limit=100 to the URL, I get a 200-response. However, according to the standard, limit is optional, so a missing limit should not fail the request. My expectation would be that the NRF either uses a default limit or sets no limit at all (I did not find anything about that in the specification).

Second issue: The response body after setting a limit is {"nfType":"","_link":{"item":null}}. That does not seem right either. If I add a valid nf-type-Parameter, the list is not empty.

nf-type however is also an optional parameter. My assumption would be that if it is not specified, all NFs are listed. However, looking at the code, it seems that if not provided, the endpoint only lists NFs with the type "" (which are none).

Am I correct with my assumption that this behaviour is not according to the specification?