Error notifications can cause React child component render failure

[andrewazores]

I wrote a fix to return a 401 error instead of 500 when the user has inadequate permissions, but it didn't affect the white screen issue. Looking in the browser log, I see this message:

Error: Minified React error #31; visit https://reactjs.org/docs/error-decoder.html?invariant=31&args[]=Error%3A%20Unauthorized&args[]= for the full message or use the non-minified dev environment for full errors and additional helpful warnings.
    React 8
    unstable_runWithPriority scheduler.production.min.js:19
    React 5
    sub AppLayout.tsx:112
    RxJS 8
    notify Notifications.tsx:65
    danger Notifications.tsx:81
    queryForTargets Targets.service.tsx:92
    RxJS 59
    checkAuth Api.service.tsx:152
    RxJS 28
    checkAuth Login.tsx:66
    handleSubmit Login.tsx:79
    handleSubmit BearerAuthForm.tsx:57
    React 10
react-dom.production.min.js:209:186
    React 5
    unstable_runWithPriority scheduler.production.min.js:19
    React 4
    unstable_runWithPriority scheduler.production.min.js:19
    React 5
    sub AppLayout.tsx:112
    RxJS 8
    notify Notifications.tsx:65
    danger Notifications.tsx:81
    queryForTargets Targets.service.tsx:92
    RxJS 59
    checkAuth Api.service.tsx:152
    RxJS 28
    checkAuth Login.tsx:66
    handleSubmit Login.tsx:79
    handleSubmit BearerAuthForm.tsx:57
    React 10

Visiting the error decoder URL gives the following message: "Objects are not valid as a React child (found: Error: Unauthorized). If you meant to render a collection of children, use an array instead."

Originally posted by @ebaron in cryostatio/cryostat#687 (comment)

[andrewazores]

The cause for this specific issue appears to be this:

cryostat-web/src/app/Shared/Services/Targets.service.tsx

Line 92 in 2f48cf5

this.notifications.danger('Target List Update Failed', err)

Here, an error occurs, and the service attempts to display a notification with an error object as the message. This will fail to render - the message must be a string. Since the error format is not necessarily well-known, a simple enough solution would be to just JSON.stringify(err) to ensure that the error is serialized to a renderable form.