CID lookup to Contact Mgr returns 'unknown' instead of nothing

Configuring a CID Lookup to use the Contact Manager will return a string of "Unknown" if the CID Number is not found. See call trace:

https://pastebin.freepbx.org/view/e26c48c0

Line 53 calls the Lookup AGI
Line 56 Sets CALLERID(name)=Unknown

Unknown is not really correct, in that the caller is not unknown since we have the CID number.

I suggest that line 56 not set CALLERID(name) to anything. If it is just left unset, then macro-user-callerid which is called later in the call flow will then set CALLERID(name) to whatever the value of CALLERID(number) is, which is more useful to display on endpoints.