[2.1] 6.12.2 HTTP Request Extension: request_header dictionary: unknown headers vs no header definition?

[sr@ctin.us]

FWD from: https://github.com/oasis-tcs/cti-stix2/issues/184

In the HTTP request extension, the request_header property is a  
optional dictionary. How do you represent "did not capture / unknown  
headers / not sharing headers in the CTI" (usually with not providing  
that property vs "no headers were provided"

Can you have an empty dictionary? (semi-related context note: empty  
Lists in STIX are not supported as per 2.12)

seems to be a carry over from work done in:  
https://github.com/oasis-tcs/cti-stix2/issues/137