[dnsdist] Correct way to ignore alterFunction callback in RemoteLogResponseAction ?

[scott McGillivray]

It's not clear in the docs how to tell RemoteLogResponseAction that you don't want to use a callback to modify the Protocol Buffer content. After some trial and error if i just type in any string it doesn't complain. 

Examples

addResponseAction(AllRule(), RemoteLogResponseAction(rl, , true))
Didn't work: Fatal error: [string "chunk"]:15: unexpected symbol near ','

addResponseAction(AllRule(), RemoteLogResponseAction(rl, true))      
Didn't work: Fatal Lua error: Unable to convert parameter from boolean to N5boost8optionalISt8functionIFvRK11DNSResponseP22DNSDistProtoBufMessageEEEE

addResponseAction(AllRule(), RemoteLogResponseAction(rl, anything, true))    
Seems to work, in as much that it didn't show error. 

Is there a correct way to do this ?

thanks.