fix(runtime-core): renderList with default value when source is undefined (#498)

packages/runtime-core/__tests__/helpers/renderList.spec.ts

@@ -41,4 +41,10 @@ describe('renderList', () => {
       renderList(iterable(), (item, index) => `node ${index}: ${item}`)
     ).toEqual(['node 0: 1', 'node 1: 2', 'node 2: 3'])
   })
+
+  it('should return empty array when source is undefined', () => {
+    expect(
+      renderList(undefined, (item, index) => `node ${index}: ${item}`)
+    ).toEqual([])
+  })
 })

packages/runtime-core/src/helpers/renderList.ts

@@ -31,6 +31,8 @@ export function renderList(
         ret[i] = renderItem(source[key], key, i)
       }
     }
+  } else {
+    ret = []
   }
-  return ret!
+  return ret
 }