From ae781091186f321b4e4ec9e84f64b6e4d5ea1043 Mon Sep 17 00:00:00 2001
From: Maxwell <145994855+ping-maxwell@users.noreply.github.com>
Date: Thu, 16 Jul 2026 16:55:23 +1000
Subject: [PATCH] fix(client): preserve null in useSession().data type with
 throw:true (#9787)

---
 .changeset/seven-sides-report.md              |  5 +
 .../better-auth/src/client/client.test.ts     | 93 +++++++++++++++++++
 .../better-auth/src/client/solid/index.ts     |  4 +-
 .../better-auth/src/client/svelte/index.ts    |  4 +-
 packages/better-auth/src/client/vanilla.ts    |  4 +-
 packages/better-auth/src/client/vue/index.ts  |  4 +-
 6 files changed, 102 insertions(+), 12 deletions(-)
 create mode 100644 .changeset/seven-sides-report.md

diff --git a/.changeset/seven-sides-report.md b/.changeset/seven-sides-report.md
new file mode 100644
index 0000000000..0f570b5f02
--- /dev/null
+++ b/.changeset/seven-sides-report.md
@@ -0,0 +1,5 @@
+---
+"better-auth": patch
+---
+
+Fixes an issue where `useSession({ throw: true })` incorrectly excluded `null` from its `data` type.
diff --git a/packages/better-auth/src/client/client.test.ts b/packages/better-auth/src/client/client.test.ts
index 2c42a8aec7..b3aff2f52a 100644
--- a/packages/better-auth/src/client/client.test.ts
+++ b/packages/better-auth/src/client/client.test.ts
@@ -393,6 +393,99 @@ describe("type", () => {
 		>();
 	});
 
+	/**
+	 * @see https://github.com/better-auth/better-auth/issues/9781
+	 */
+	describe("useSession().data with nullable types", () => {
+		it("useSession().data should be nullable with `throw:true` - react", () => {
+			const client = createReactClient({
+				plugins: [testClientPlugin()],
+				baseURL: "http://localhost:3000",
+				fetchOptions: {
+					throw: true,
+					customFetchImpl: async (url, init) => {
+						return new Response();
+					},
+				},
+			});
+
+			type UseSessionReturn = ReturnType<typeof client.useSession>;
+			type DataField = UseSessionReturn["data"];
+			expectTypeOf<null>().toMatchTypeOf<DataField>();
+		});
+
+		it("useSession().data should be nullable with `throw:true` - vue", () => {
+			const client = createVueClient({
+				plugins: [testClientPlugin()],
+				baseURL: "http://localhost:3000",
+				fetchOptions: {
+					throw: true,
+					customFetchImpl: async (url, init) => {
+						return new Response();
+					},
+				},
+			});
+
+			const session = client.useSession();
+			type DataField = (typeof session)["value"]["data"];
+			expectTypeOf<null>().toMatchTypeOf<DataField>();
+		});
+
+		it("useSession().data should be nullable with `throw:true` - solid", () => {
+			const client = createSolidClient({
+				plugins: [testClientPlugin()],
+				baseURL: "http://localhost:3000",
+				fetchOptions: {
+					throw: true,
+					customFetchImpl: async (url, init) => {
+						return new Response();
+					},
+				},
+			});
+
+			type UseSession = ReturnType<typeof client.useSession>;
+			type UseSessionReturn = ReturnType<UseSession>;
+			type DataField = UseSessionReturn["data"];
+			expectTypeOf<null>().toMatchTypeOf<DataField>();
+		});
+
+		it("useSession().data should be nullable with `throw:true` - svelte", () => {
+			const client = createSvelteClient({
+				plugins: [testClientPlugin()],
+				baseURL: "http://localhost:3000",
+				fetchOptions: {
+					throw: true,
+					customFetchImpl: async (url, init) => {
+						return new Response();
+					},
+				},
+			});
+
+			type UseSessionAtom = ReturnType<typeof client.useSession>;
+			type UseSessionReturn = ReturnType<UseSessionAtom["get"]>;
+			type DataField = UseSessionReturn["data"];
+			expectTypeOf<null>().toMatchTypeOf<DataField>();
+		});
+
+		it("useSession().data should be nullable with `throw:true` - vanilla", () => {
+			const client = createVanillaClient({
+				plugins: [testClientPlugin()],
+				baseURL: "http://localhost:3000",
+				fetchOptions: {
+					throw: true,
+					customFetchImpl: async (url, init) => {
+						return new Response();
+					},
+				},
+			});
+
+			type UseSessionAtom = typeof client.useSession;
+			type UseSessionReturn = ReturnType<UseSessionAtom["get"]>;
+			type DataField = UseSessionReturn["data"];
+			expectTypeOf<null>().toMatchTypeOf<DataField>();
+		});
+	});
+
 	it("should infer `error` schema correctly", async () => {
 		const client = createSolidClient({
 			plugins: [testClientPlugin()],
diff --git a/packages/better-auth/src/client/solid/index.ts b/packages/better-auth/src/client/solid/index.ts
index 939c22a4cb..3ca4f1126f 100644
--- a/packages/better-auth/src/client/solid/index.ts
+++ b/packages/better-auth/src/client/solid/index.ts
@@ -51,9 +51,7 @@ type ClientSession<Option extends BetterAuthClientOptions> =
 	}
 		? Res extends BetterFetchResponse<infer S>
 			? S
-			: Res extends Record<string, any>
-				? Res
-				: never
+			: Res
 		: never;
 
 /**
diff --git a/packages/better-auth/src/client/svelte/index.ts b/packages/better-auth/src/client/svelte/index.ts
index 51f57608a8..f3b403e252 100644
--- a/packages/better-auth/src/client/svelte/index.ts
+++ b/packages/better-auth/src/client/svelte/index.ts
@@ -46,9 +46,7 @@ type ClientSession<Option extends BetterAuthClientOptions> =
 	}
 		? Res extends BetterFetchResponse<infer S>
 			? S
-			: Res extends Record<string, any>
-				? Res
-				: never
+			: Res
 		: never;
 
 /**
diff --git a/packages/better-auth/src/client/vanilla.ts b/packages/better-auth/src/client/vanilla.ts
index afc8c9039b..7497ed7bc1 100644
--- a/packages/better-auth/src/client/vanilla.ts
+++ b/packages/better-auth/src/client/vanilla.ts
@@ -46,9 +46,7 @@ type ClientSession<Option extends BetterAuthClientOptions> =
 	}
 		? Res extends BetterFetchResponse<infer S>
 			? S
-			: Res extends Record<string, any>
-				? Res
-				: never
+			: Res
 		: never;
 
 /**
diff --git a/packages/better-auth/src/client/vue/index.ts b/packages/better-auth/src/client/vue/index.ts
index 5edc22068b..adad830491 100644
--- a/packages/better-auth/src/client/vue/index.ts
+++ b/packages/better-auth/src/client/vue/index.ts
@@ -53,9 +53,7 @@ type ClientSession<Option extends BetterAuthClientOptions> =
 	}
 		? Res extends BetterFetchResponse<infer S>
 			? S
-			: Res extends Record<string, any>
-				? Res
-				: never
+			: Res
 		: never;
 
 type VueUseSession<Option extends BetterAuthClientOptions> = {