From 3cdb4bd744ec6180550510523c0757e740cc6afc Mon Sep 17 00:00:00 2001
From: Jean-Marc Le Roux <jeanmarc@lx.industries>
Date: Sat, 30 Aug 2025 14:45:29 +0200
Subject: [PATCH] fix: return undefined for optional arrays instead of empty
 arrays

- Update generateDefaultValue to return undefined for optional array parameters
- Add comprehensive tests for required vs non-required arrays
- Fixes issue where MCP Inspector sends empty arrays [] for optional parameters
- Resolves compatibility issues with OpenAPI servers expecting omitted optionals

Refs #771
---
 client/src/utils/__tests__/schemaUtils.test.ts | 18 ++++++++++++++----
 client/src/utils/schemaUtils.ts                |  2 +-
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/client/src/utils/__tests__/schemaUtils.test.ts b/client/src/utils/__tests__/schemaUtils.test.ts
index 0ecd8075..50337532 100644
--- a/client/src/utils/__tests__/schemaUtils.test.ts
+++ b/client/src/utils/__tests__/schemaUtils.test.ts
@@ -39,8 +39,8 @@ describe("generateDefaultValue", () => {
     ).toBe(false);
   });
 
-  test("generates default array", () => {
-    expect(generateDefaultValue({ type: "array" })).toEqual([]);
+  test("generates undefined for optional array", () => {
+    expect(generateDefaultValue({ type: "array" })).toBe(undefined);
   });
 
   test("generates default empty object", () => {
@@ -52,8 +52,18 @@ describe("generateDefaultValue", () => {
     expect(generateDefaultValue({ type: "unknown" })).toBe(undefined);
   });
 
-  test("generates empty array for non-required array", () => {
-    expect(generateDefaultValue({ type: "array" })).toEqual([]);
+  test("generates empty array for required array", () => {
+    const parentSchema = { required: ["testArray"] };
+    expect(
+      generateDefaultValue({ type: "array" }, "testArray", parentSchema),
+    ).toEqual([]);
+  });
+
+  test("generates undefined for non-required array", () => {
+    const parentSchema = { required: ["otherField"] };
+    expect(
+      generateDefaultValue({ type: "array" }, "testArray", parentSchema),
+    ).toBe(undefined);
   });
 
   test("generates empty object for non-required object", () => {
diff --git a/client/src/utils/schemaUtils.ts b/client/src/utils/schemaUtils.ts
index 7a175142..02603d0e 100644
--- a/client/src/utils/schemaUtils.ts
+++ b/client/src/utils/schemaUtils.ts
@@ -109,7 +109,7 @@ export function generateDefaultValue(
     case "boolean":
       return isRequired ? false : undefined;
     case "array":
-      return [];
+      return isRequired ? [] : undefined;
     case "object": {
       if (!schema.properties) return {};