Handle undefined value in Debug view of Array and Object

Fixes #2696

packages/node_modules/@node-red/util/lib/util.js

@@ -771,6 +771,11 @@ function encodeObject(msg,opts) {
                             } else if (value.constructor.name === "Socket") {
                                 value = "[internal]"
                             }
+                        } else if (value === undefined) {
+                            value = {
+                                __enc__: true,
+                                type: "undefined",
+                            }
                         }
                         return value;
                     }," ");