报错viewer3D.js:45952 Uncaught TypeError: Cannot read property 'getSelection' of undefined

at GuiViewer3D.Viewer3D.getSelection (viewer3D.js:45952)
at ViewerPropertyPanel.initialize (viewer3D.js:55068)
at ViewerPropertyPanel.DockingPanel (viewer3D.js:37943)
at ViewerPropertyPanel.PropertyPanel [as constructor] (viewer3D.js:38930)
at new ViewerPropertyPanel (viewer3D.js:55016)
at GuiViewer3D.getPropertyPanel (viewer3D.js:51523)
at index.html:75
代码：
const propPanel = viewer.getPropertyPanel( true );
propPanel.addProperty( '所属房名', '课厅', '其他' );