fix: TypeError custom override (#1229)

* fix: enum string escape can be nullable

* fix: returntype on custom mock

Author: dipsaus9

packages/mock/src/msw/index.ts

@@ -81,7 +81,7 @@ export const generateMSW = (
   const handlerName = `get${pascal(operationId)}MockHandler`;
 
   const mockImplementation = isReturnHttpResponse
-    ? `export const ${getResponseMockFunctionName} = (${isResponseOverridable ? `overrideResponse: any = {}` : ''}): ${returnType} => (${value})\n\n`
+    ? `export const ${getResponseMockFunctionName} = (${isResponseOverridable ? `overrideResponse: any = {}` : ''})${mockData ? '' : `: ${returnType}`} => (${value})\n\n`
     : '';
 
   const handlerImplementation = `

tests/configs/default.config.ts

@@ -102,4 +102,24 @@ export default defineConfig({
       target: '../generated/default/example-v3-1/endpoints.ts',
     },
   },
+  'override-mock': {
+    input: '../specifications/petstore.yaml',
+    output: {
+      mode: 'split',
+      mock: true,
+      schemas: '../generated/default/override-mock/model',
+      target: '../generated/default/override-mock/endpoints.ts',
+      override: {
+        operations: {
+          listPets: {
+            mock: {
+              data: () => {
+                return {};
+              },
+            },
+          },
+        },
+      },
+    },
+  },
 });