Set filter to undefined when it's empty on findExceptionLists method (#128455)

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

packages/kbn-securitysolution-list-api/src/api/index.ts

@@ -231,7 +231,7 @@ const fetchExceptionLists = async ({
   signal,
 }: ApiCallFetchExceptionListsProps): Promise<FoundExceptionListSchema> => {
   const query = {
-    filter: filters,
+    filter: filters || undefined,
     namespace_type: namespaceTypes,
     page: pagination.page ? `${pagination.page}` : '1',
     per_page: pagination.perPage ? `${pagination.perPage}` : '20',

x-pack/plugins/lists/public/exceptions/api.test.ts

@@ -278,6 +278,31 @@ describe('Exceptions Lists API', () => {
       expect(exceptionResponse.data).toEqual([getExceptionListSchemaMock()]);
     });
 
+    test('it returns expected exception lists when empty filter', async () => {
+      const exceptionResponse = await fetchExceptionLists({
+        filters: '',
+        http: httpMock,
+        namespaceTypes: 'single,agnostic',
+        pagination: {
+          page: 1,
+          perPage: 20,
+        },
+        signal: abortCtrl.signal,
+      });
+      expect(httpMock.fetch).toHaveBeenCalledWith('/api/exception_lists/_find', {
+        method: 'GET',
+        query: {
+          namespace_type: 'single,agnostic',
+          page: '1',
+          per_page: '20',
+          sort_field: 'exception-list.created_at',
+          sort_order: 'desc',
+        },
+        signal: abortCtrl.signal,
+      });
+      expect(exceptionResponse.data).toEqual([getExceptionListSchemaMock()]);
+    });
+
     test('it returns error if response payload fails decode', async () => {
       const badPayload = getExceptionListSchemaMock();
       // @ts-expect-error