fix(client): preserve null in useSession().data type with throw:true (#9787)

.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.

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()],

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;
 
 /**

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;
 
 /**

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;
 
 /**

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> = {