Rudder

Not sure if it's the parent correction that lead to that problem (but likely), but now, in the case where:

- we have a mandatory string parameter, say udp_open_ports (in firewall technique),
- the parameter is given in directive with ${node.properties[udp_open_ports] | default=" "}
- the node doesn't have the property defined,

Then we get the following error:

⇨ Cannot build target configuration node; 
    cause was: Error while computing Node Configuration for nodes: ; 
    cause was: Unexpected: Accumulated: Unexpected: Error with parameters expansion for node 'xxxxxx' (xxxxxx); 
    cause was: Unexpected: Inconsistency: Error for policy for directive 'Firewall' [xxxxx] in rule 'Firewall' [xxxxx]: a non optional value is missing for parameter 'udp_open_ports' [param ID: 3021FC4F-DA33-4D84-8991-C42EBAB2335F] ;