It's a bit unusual to remove a parameter value that you're passing to a child component, but if you do, our upcoming hot-reload-refresh mechanism doesn't yet account for it.

Repro: In the default project template, in Index.razor, change this:

<SurveyPrompt Title="How is Blazor working for you?" />

... to this:

<SurveyPrompt />

No change will show up in the UI. This is because the existing SurveyPrompt instance already has a value for its Title property. Failing to supply a new value just means that the old one doesn't get overwritten.

Expected resolution

We can't control how all IComponent types deal with the removal of an incoming parameter value, but for ComponentBase at least, we can add some logic to SetParametersAsync that checks the IsHotReload flag and, if found, runs through some new code path to default-out all of its [Parameter] properties before receiving the new set from its parent.

Severity

Low. I don't think this is a common scenario at all.