fix: refactoring code

Author: zyao89

src/service/chainConfig.js

@@ -80,8 +80,10 @@ module.exports = function chainDefault(api, vueConfig, _mapi) {
     // webpack 所有配置合入
     const _service = api.service;
     // 覆盖逻辑
-    const originaFn = _service.resolveWebpackConfig;
-    _service.resolveWebpackConfig = function(chainableConfig) {
-        return _mapi.resolveWebpackConfig(originaFn.apply(_service, chainableConfig));
-    };
+    if (_service) {
+        const originaFn = _service.resolveWebpackConfig;
+        _service.resolveWebpackConfig = function(chainableConfig) {
+            return _mapi.resolveWebpackConfig(originaFn.apply(_service, chainableConfig));
+        };
+    }
 };

test/cliPlugin.spec.js

@@ -11,6 +11,7 @@ describe('Vue CLI Plugin', () => {
             chainWebpack() {
 
             },
+            service: {},
         };
 
         plugin(api, {});