Not reproducable, but I got this error after editing the user settings (added a setting).
workbench.main.js:2913 Unable to open 'Workspace Settings': Cannot read property 'getAssociatedPreferencesModel' of null.: Error: Unable to open 'Workspace Settings': Cannot read property 'getAssociatedPreferencesModel' of null.
at t.doHandleSetInputError (file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:4186:761)
at file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:4186:362
at n.Class.derive._creator.then (file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:146:770)
at t.doSetInput (file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:4186:124)
at t.doOpenEditor (file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:4184:617)
at t.openEditor (file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:4183:736)
at e.doOpenEditor (file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:3195:443)
at e.openEditor (file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:3194:916)
at file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:3638:838
at Object.g [as _notify] (file:///C:/Program Files/Microsoft VS Code Insiders/resources/app/out/vs/workbench/workbench.main.js:140:868)
Not reproducable, but I got this error after editing the user settings (added a setting).