diff --git a/package-lock.json b/package-lock.json
index e685135e..d6110935 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -39,6 +39,7 @@
         "eslint": "^9",
         "eslint-config-next": "^16.1.6",
         "jsdom": "^28.1.0",
+        "mitata": "^1.0.34",
         "server-only": "^0.0.1",
         "tailwindcss": "^4",
         "typescript": "^5",
@@ -7420,6 +7421,13 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/mitata": {
+      "version": "1.0.34",
+      "resolved": "https://registry.npmjs.org/mitata/-/mitata-1.0.34.tgz",
+      "integrity": "sha512-Mc3zrtNBKIMeHSCQ0XqRLo1vbdIx1wvFV9c8NJAiyho6AjNfMY8bVhbS12bwciUdd1t4rj8099CH3N3NFahaUA==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/ms": {
       "version": "2.1.3",
       "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.3.tgz",
diff --git a/package.json b/package.json
index bba07435..5b46f424 100644
--- a/package.json
+++ b/package.json
@@ -43,6 +43,7 @@
     "eslint": "^9",
     "eslint-config-next": "^16.1.6",
     "jsdom": "^28.1.0",
+    "mitata": "^1.0.34",
     "server-only": "^0.0.1",
     "tailwindcss": "^4",
     "typescript": "^5",
diff --git a/src/lib/__tests__/githubYearInReview.test.ts b/src/lib/__tests__/githubYearInReview.test.ts
index f89b1ac8..20b8f84b 100644
--- a/src/lib/__tests__/githubYearInReview.test.ts
+++ b/src/lib/__tests__/githubYearInReview.test.ts
@@ -393,6 +393,21 @@ describe("fetchYearInReviewData safety checks", () => {
 });
 
 describe("fetchYearInReviewData additional coverage", () => {
+    it("throws 500 GitHubApiError for non-Error thrown objects", async () => {
+        mockFetch.mockImplementation(() => {
+            throw "String error";
+        });
+
+        await expect(fetchYearInReviewData("testuser", 2024, "fake-token")).rejects.toThrow(GitHubApiError);
+        try {
+            await fetchYearInReviewData("testuser", 2024, "fake-token");
+        } catch (error) {
+            expect(error).toBeInstanceOf(GitHubApiError);
+            expect((error as GitHubApiError).status).toBe(500);
+            expect((error as GitHubApiError).message).toBe("Failed to fetch year in review data");
+        }
+    });
+
     it("throws 500 GitHubApiError for unknown errors", async () => {
         mockFetch.mockImplementation(() => {
             throw new Error("Unexpected crash");
@@ -592,25 +607,123 @@ describe("githubYearInReview additional edge cases", () => {
     });
 
     it("fetchCommitDatesForTopRepos handles missing defaultBranchRef or history", async () => {
-        mockFetch.mockImplementation(() => {
-            return Promise.resolve(jsonResponse({
-                data: {
-                    user: {
-                        id: "123",
-                        contributionsCollection: {
-                            totalCommitContributions: 1,
-                            contributionCalendar: { totalContributions: 1, weeks: [] },
-                            commitContributionsByRepository: [
-                                { repository: { owner: { login: "u" }, name: "r" }, contributions: { totalCount: 1 } }
-                            ]
+        let callCount = 0;
+        mockFetch.mockImplementation((url) => {
+            const urlStr = typeof url === "string" ? url : url instanceof URL ? url.toString() : url.url;
+            if (urlStr.includes("/graphql")) {
+                callCount++;
+                if (callCount === 1) {
+                    return Promise.resolve(jsonResponse({
+                        data: {
+                            user: {
+                                id: "u1",
+                                contributionsCollection: {
+                                    totalCommitContributions: 10,
+                                    totalPullRequestContributions: 0,
+                                    totalIssueContributions: 0,
+                                    totalPullRequestReviewContributions: 0,
+                                    contributionCalendar: {
+                                        totalContributions: 10,
+                                        weeks: []
+                                    },
+                                    commitContributionsByRepository: [
+                                        { repository: { name: "repo", owner: { login: "u" } }, contributions: { totalCount: 10 } }
+                                    ]
+                                }
+                            }
                         }
-                    },
-                    repo0: { defaultBranchRef: null } // Missing defaultBranchRef
+                    }));
                 }
-            }));
+                return Promise.resolve(jsonResponse({
+                    data: {
+                        repo0: { defaultBranchRef: null }
+                    }
+                }));
+            }
+            return Promise.resolve(jsonResponse([], 200));
         });
 
         const data = await fetchYearInReviewData("user", 2024, "token");
         expect(data.year).toBe(2024);
     });
+
+    it("fetchCommitDatesForTopRepos handles nodes without author or date", async () => {
+        let callCount = 0;
+        mockFetch.mockImplementation((url) => {
+            const urlStr = typeof url === "string" ? url : url instanceof URL ? url.toString() : url.url;
+            if (urlStr.includes("/graphql")) {
+                callCount++;
+                if (callCount === 1) {
+                    return Promise.resolve(jsonResponse({
+                        data: {
+                            user: {
+                                id: "u1",
+                                contributionsCollection: {
+                                    totalCommitContributions: 10,
+                                    totalPullRequestContributions: 0,
+                                    totalIssueContributions: 0,
+                                    totalPullRequestReviewContributions: 0,
+                                    contributionCalendar: {
+                                        totalContributions: 10,
+                                        weeks: []
+                                    },
+                                    commitContributionsByRepository: [
+                                        { repository: { name: "repo", owner: { login: "u" } }, contributions: { totalCount: 10 } }
+                                    ]
+                                }
+                            }
+                        }
+                    }));
+                }
+                return Promise.resolve(jsonResponse({
+                    data: {
+                        repo0: { defaultBranchRef: { target: { history: { nodes: [{ author: null }, { author: { date: null } }, { author: { date: "2024-01-01T12:00:00Z" } }] } } } }
+                    }
+                }));
+            }
+            return Promise.resolve(jsonResponse([], 200));
+        });
+        const data = await fetchYearInReviewData("user", 2024, "token");
+        expect(data.year).toBe(2024);
+    });
+
+    it("fetchCommitDatesForTopRepos handles null nodes in history", async () => {
+        let callCount = 0;
+        mockFetch.mockImplementation((url) => {
+            const urlStr = typeof url === "string" ? url : url instanceof URL ? url.toString() : url.url;
+            if (urlStr.includes("/graphql")) {
+                callCount++;
+                if (callCount === 1) {
+                    return Promise.resolve(jsonResponse({
+                        data: {
+                            user: {
+                                id: "u1",
+                                contributionsCollection: {
+                                    totalCommitContributions: 10,
+                                    totalPullRequestContributions: 0,
+                                    totalIssueContributions: 0,
+                                    totalPullRequestReviewContributions: 0,
+                                    contributionCalendar: {
+                                        totalContributions: 10,
+                                        weeks: []
+                                    },
+                                    commitContributionsByRepository: [
+                                        { repository: { name: "repo", owner: { login: "u" } }, contributions: { totalCount: 10 } }
+                                    ]
+                                }
+                            }
+                        }
+                    }));
+                }
+                return Promise.resolve(jsonResponse({
+                    data: {
+                        repo0: { defaultBranchRef: { target: { history: { nodes: [null, { author: { date: "2024-01-01T12:00:00Z" } }] } } } }
+                    }
+                }));
+            }
+            return Promise.resolve(jsonResponse([], 200));
+        });
+        const data = await fetchYearInReviewData("user", 2024, "token");
+        expect(data.year).toBe(2024);
+    });
 });
diff --git a/src/lib/githubYearInReview.ts b/src/lib/githubYearInReview.ts
index 23c4538d..a3539d07 100644
--- a/src/lib/githubYearInReview.ts
+++ b/src/lib/githubYearInReview.ts
@@ -196,16 +196,17 @@ async function fetchCommitDatesForTopRepos(
         const response = await graphql<Record<string, unknown>>(query, token, variables);
         const dates: string[] = [];
 
+        type RepoGraphQLNode = {
+            defaultBranchRef?: { target?: { history?: { nodes?: Array<{ author?: { date?: string } }> } } };
+        };
+
         for (let i = 0; i < candidates.length; i++) {
-            const repoData = response[`repo${i}`] as Record<string, unknown> | undefined;
-            const defaultBranchRef = repoData?.defaultBranchRef as Record<string, unknown> | undefined;
-            const target = defaultBranchRef?.target as Record<string, unknown> | undefined;
-            const history = target?.history as Record<string, unknown> | undefined;
-            const historyNodes = (history?.nodes as Array<Record<string, unknown>> | undefined) || [];
-            for (const node of historyNodes) {
-                const author = node?.author as Record<string, unknown> | undefined;
-                if (typeof author?.date === 'string') {
-                    dates.push(author.date);
+            const nodes = (response[`repo${i}`] as RepoGraphQLNode | undefined)?.defaultBranchRef?.target?.history?.nodes;
+            if (!nodes) continue;
+            for (let j = 0; j < nodes.length; j++) {
+                const date = nodes[j]?.author?.date;
+                if (typeof date === 'string') {
+                    dates.push(date);
                 }
             }
         }