diff --git a/gatsby-node.ts b/gatsby-node.ts
index 0afa3f4b..d196b6cd 100644
--- a/gatsby-node.ts
+++ b/gatsby-node.ts
@@ -80,7 +80,12 @@ export const createPages: GatsbyNode["createPages"] = async (api) => {
     return;
   }
 
-  const pages = res.data?.allMarkdownRemark.nodes!;
+  const pages = res.data?.allMarkdownRemark.nodes;
+  if (!pages) {
+    api.reporter.error("unreachable");
+    return;
+  }
+
   const component = path.resolve("src/templates/blog-post.tsx");
   for (let i = 0; i < pages.length; ++i) {
     const slug = path.basename(pages[i].parent.name);
diff --git a/src/components/date.test.tsx b/src/components/date.test.tsx
index e3e717ac..7951e9cb 100644
--- a/src/components/date.test.tsx
+++ b/src/components/date.test.tsx
@@ -1,5 +1,6 @@
 import { expect, it } from "vitest";
 import { DateString } from "./date";
+import React from "react";
 import { render } from "../../utils/react-test";
 
 it("renders correctly", () => {
diff --git a/src/components/footer.test.tsx b/src/components/footer.test.tsx
index 701bcd04..d9139a95 100644
--- a/src/components/footer.test.tsx
+++ b/src/components/footer.test.tsx
@@ -1,5 +1,6 @@
 import { expect, it } from "vitest";
 import { Footer } from "./footer";
+import React from "react";
 import { render } from "../../utils/react-test";
 
 it("renders correctly", () => {
diff --git a/src/components/header.test.tsx b/src/components/header.test.tsx
index 5ef6f16d..7254fb99 100644
--- a/src/components/header.test.tsx
+++ b/src/components/header.test.tsx
@@ -1,5 +1,6 @@
 import { expect, it } from "vitest";
 import { Header } from "./header";
+import React from "react";
 import { render } from "../../utils/react-test";
 
 it("renders correctly", () => {
diff --git a/src/components/navigation.test.tsx b/src/components/navigation.test.tsx
index 89a59d42..5143f3f7 100644
--- a/src/components/navigation.test.tsx
+++ b/src/components/navigation.test.tsx
@@ -1,5 +1,6 @@
 import { expect, it } from "vitest";
 import { Navigation } from "./navigation";
+import React from "react";
 import { render } from "../../utils/react-test";
 
 it("renders correctly", () => {
diff --git a/src/components/prev-next-link.test.tsx b/src/components/prev-next-link.test.tsx
index 60d4c990..97e339a7 100644
--- a/src/components/prev-next-link.test.tsx
+++ b/src/components/prev-next-link.test.tsx
@@ -1,5 +1,6 @@
 import { expect, it } from "vitest";
 import { PrevNextLink } from "./prev-next-link";
+import React from "react";
 import { render } from "../../utils/react-test";
 
 it("renders both prev and next correctly", () => {
diff --git a/src/components/questions.test.tsx b/src/components/questions.test.tsx
index dcf1790d..1f5dc46a 100644
--- a/src/components/questions.test.tsx
+++ b/src/components/questions.test.tsx
@@ -1,5 +1,6 @@
 import { expect, it } from "vitest";
 import { Questions } from "./questions";
+import React from "react";
 import { render } from "../../utils/react-test";
 
 it("renders correctly", () => {
diff --git a/src/components/sns-link.test.tsx b/src/components/sns-link.test.tsx
index ec8b9491..68650d4e 100644
--- a/src/components/sns-link.test.tsx
+++ b/src/components/sns-link.test.tsx
@@ -1,4 +1,5 @@
 import { expect, it } from "vitest";
+import React from "react";
 import { SNSLink } from "./sns-link";
 import { render } from "../../utils/react-test";
 
diff --git a/src/components/title.test.tsx b/src/components/title.test.tsx
index 7a759cba..7305ef57 100644
--- a/src/components/title.test.tsx
+++ b/src/components/title.test.tsx
@@ -1,5 +1,6 @@
 import { Subtitle, Title } from "./title";
 import { expect, it } from "vitest";
+import React from "react";
 import { render } from "../../utils/react-test";
 
 it("renders title correctly", () => {
diff --git a/src/pages/blog.tsx b/src/pages/blog.tsx
index cf0013ab..14d2a08a 100644
--- a/src/pages/blog.tsx
+++ b/src/pages/blog.tsx
@@ -19,6 +19,8 @@ function BlogCard({
   parent,
 }: Queries.BlogEntriesQuery["allMarkdownRemark"]["nodes"][number]): JSX.Element {
   const title = frontmatter?.title ?? "無題";
+  // NOTE: it will be fixed in PR #395.
+  // eslint-disable-next-line @typescript-eslint/no-non-null-asserted-optional-chain
   const slug = (parent as { name?: string })?.name!;
   return (
     <HStack borderColor="shadowed" borderRightWidth="1px" borderBottomWidth="2px">