policy-node.lua: Fix nil value indexing
Fixes the warning:
[string "policy-node.lua"]:117: attempt to index a nil value (field '?') stack traceback: [string "policy-node.lua"]:117: in function <[string "policy-node.lua"]:109>
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Fixes the warning:
[string "policy-node.lua"]:117: attempt to index a nil value (field '?') stack traceback: [string "policy-node.lua"]:117: in function <[string "policy-node.lua"]:109>