diff --git a/src/components/inspector.tsx b/src/components/inspector.tsx
index a6db620..4ddacf9 100644
--- a/src/components/inspector.tsx
+++ b/src/components/inspector.tsx
@@ -765,7 +765,7 @@ const NodeInspector: FC = () => {
             rules={[
               {
                 validator() {
-                  if (def.group && usingGroups && !usingGroups[def.group]) {
+                  if (def.group && !usingGroups[def.group]) {
                     return Promise.reject(new Error(t("node.invalidGroup", { group: def.group })));
                   }
                   return Promise.resolve();
diff --git a/src/components/register-node.ts b/src/components/register-node.ts
index 7dd14cc..1fcc6c5 100644
--- a/src/components/register-node.ts
+++ b/src/components/register-node.ts
@@ -150,7 +150,7 @@ G6.registerNode(
         !nodeDefs.has(data.name) ||
         (data.path && !data.children?.length) ||
         !checkTreeData(data) ||
-        (nodeDef.group && usingGroups && !usingGroups[nodeDef.group]) ||
+        (nodeDef.group && !usingGroups[nodeDef.group]) ||
         (usingVars && data.input?.some((v) => !usingVars![v])) ||
         (usingVars && data.output?.some((v) => !usingVars![v])) ||
         (usingVars &&
diff --git a/src/misc/b3util.ts b/src/misc/b3util.ts
index 5e58ec3..57f1493 100644
--- a/src/misc/b3util.ts
+++ b/src/misc/b3util.ts
@@ -26,7 +26,7 @@ export class NodeDefs extends Map<string, NodeDef> {
 
 export let nodeDefs: NodeDefs = new NodeDefs();
 export let groupDefs: string[] = [];
-export let usingGroups: Record<string, boolean> | null = null;
+export let usingGroups: Record<string, boolean> = {};
 export let usingVars: Record<string, VarDef> | null = null;
 
 const parsedExprs: Record<string, string[]> = {};
@@ -58,7 +58,7 @@ export const initWorkdir = (path: string, handler: typeof alertError) => {
 };
 
 export const updateUsingGroups = (group: string[]) => {
-  usingGroups = null;
+  usingGroups = {};
   for (const g of group) {
     usingGroups ??= {};
     usingGroups[g] = true;