fixed issue where no root node needs to be defined in JSON definition

src/BehaviourTreeDefinitionValidator.ts

@@ -230,6 +230,11 @@ function validateNode(definition: any, depth: number): void {
         );
     }
 
+    // If this node is at the very base of the definition then it MUST be a root node.
+    if (depth === 0 && definition.type !== "root") {
+        throw new Error(`expected root node at base of definition but got node of type '${definition.type}'`);
+    }
+
     // How we validate this node definition will depend on its type.
     switch (definition.type) {
         case "action":

test/BehaviourTreeDefinitionValidator.spec.ts

@@ -46,6 +46,31 @@ describe("The validateDefinition function takes a tree definition as an argument
             });
         });
 
+        describe("the root node in the definition is not actually a root node", () => {
+            it("(MDSL)", () => {
+                verifyResult("action [noop]", false, "expected root node at base of definition");
+            });
+
+            it("(JSON)", () => {
+                const definition = {
+                    type: "action",
+                    call: "noop"
+                };
+
+                // The definition can be either an array (of root node definitions) or an object (the single primary root node definition), verify both.
+                verifyResult(
+                    definition,
+                    false,
+                    "expected root node at base of definition but got node of type 'action'"
+                );
+                verifyResult(
+                    [definition],
+                    false,
+                    "expected root node at base of definition but got node of type 'action'"
+                );
+            });
+        });
+
         describe("there are duplicate root node identifiers", () => {
             it("(MDSL)", () => {
                 verifyResult(