fix: batching with zod .optional() input

packages/server/src/procedure.ts

@@ -57,19 +57,37 @@ export abstract class Procedure<
     this.inputParser = opts.inputParser;
   }
 
+  private execParser(fn: (v: unknown) => TInput, rawInput: unknown): TInput {
+    if (rawInput !== null) {
+      return fn(rawInput);
+    }
+    // do potentially second pass to see if we can parse it as `undefined` if rawInput was `null`
+    // this is because JSON.stringify() will convert e.g. [undefined] to [null]
+    // https://github.com/trpc/trpc/pull/669
+    try {
+      return fn(rawInput);
+    } catch (err) {
+      try {
+        return fn(undefined);
+      } catch {
+        throw err;
+      }
+    }
+  }
+
   private parseInput(rawInput: unknown): TInput {
     try {
       const parser: any = this.inputParser;
 
       if (typeof parser === 'function') {
-        return parser(rawInput);
+        return this.execParser(parser, rawInput);
       }
       if (typeof parser.parse === 'function') {
-        return parser.parse(rawInput);
+        return this.execParser(parser.parse, rawInput);
       }
 
       if (typeof parser.validateSync === 'function') {
-        return parser.validateSync(rawInput);
+        return this.execParser(parser.validateSync, rawInput);
       }
 
       throw new Error('Could not find a validator fn');

packages/server/test/index.test.tsx

@@ -595,3 +595,34 @@ describe('TRPCAbortError', () => {
     close();
   });
 });
+
+test('regression: JSON.stringify([undefined]) gives [null] causes wrong type to procedure input', async () => {
+  const { client, close } = routerToServerAndClient(
+    trpc.router().query('q', {
+      input: z.string().optional(),
+      async resolve({ input }) {
+        return { input };
+      },
+    }),
+    {
+      client({ httpUrl }) {
+        return {
+          links: [httpBatchLink({ url: httpUrl })],
+        };
+      },
+      server: {
+        batching: {
+          enabled: true,
+        },
+      },
+    },
+  );
+
+  expect(await client.query('q', 'foo')).toMatchInlineSnapshot(`
+Object {
+  "input": "foo",
+}
+`);
+  expect(await client.query('q')).toMatchInlineSnapshot(`Object {}`);
+  close();
+});