无法将值“<unknown>”分配给属性 'XXX'

Unable to assign value '<unknown>' to attribute 'XXX'

我正在尝试将项目部署到 App Engine,但如果我在 app.yaml 中使用“ü”字符作为值,则会收到以下错误。我不想 HTML/URL 对值进行编码。有什么办法可以克服这个问题吗?

ERROR: (gcloud.app.deploy) An error occurred while parsing file: [app.yaml]
Unable to assign value '<unknown>' to attribute 'XXX':
Value u'\xfc' for XXX could not be converted to type str.

app.yaml 文件:

runtime: php72
env: standard

env_variables: 
  XXX: "ü"

我已经创建了一张 Google 支持票,我收到了以下回复。

Upon investigating this issue, I found that the only available workaround is to load an ASCII representation of the non-ASCII characters and then transform within the app's logic.

Additionally, I found that a Feature Request already exist for this issue, but currently there is not an ETA for its implementation or guaranty that it will be done.