代码拉取完成，页面将自动刷新
版本：编译自 20210426 的 release 分支
在流程表单编辑页面，点击预览按钮，显示空白。
Console提示错误：
Uncaught SyntaxError: JSON.parse: unexpected character at line 1 column 2 of the JSON data
initialize preview.html:1
initialize mootools-1.6.0_all.js:7078
i mootools-1.6.0_all.js:1384
r mootools-1.6.0_all.js:1342
load preview.html:34
_runCallback o2.js:233
onSuccess o2.js:1114
fireEvent mootools-1.6.0_all.js:1505
d mootools-1.6.0_all.js:235
each mootools-1.6.0_all.js:345
fireEvent mootools-1.6.0_all.js:1503
i mootools-1.6.0_all.js:1384
onSuccess mootools-1.6.0_all.js:6323
i mootools-1.6.0_all.js:1384
success mootools-1.6.0_all.js:6318
i mootools-1.6.0_all.js:1384
onStateChange mootools-1.6.0_all.js:6298
i mootools-1.6.0_all.js:1384
