如何修复values.xml：227：错误：<item>内部元素必须是资源引用或为空

Question

Android resource compilation failed
C:\Projects\sources\Teach Zoner-2\app\build\intermediates\incremental\mergeDebugResources\merged.dir\values\values.xml:227: error: <item> inner element must either be a resource reference or empty.
C:\Projects\sources\Teach Zoner-2\app\build\intermediates\incremental\mergeDebugResources\merged.dir\values\values.xml:235: error: <item> inner element must either be a resource reference or empty.
C:\Projects\sources\Teach Zoner-2\app\build\intermediates\incremental\mergeDebugResources\merged.dir\values\values.xml: error: file failed to compile.