Properties: Hint on empty frontmatter content, or provide a corresponding UI

Use case or problem

When deleting all properties of a note programmatically, I intended to leave an empty object, to indicate that this note needs some properties but is left empty temporarily. Then the frontmatter in the source mode would look like

---
{}
---

or

---
---

I thought there would be a UI with no property line and only an Add property button in both reading and live preview modes. However, currently, nothing would shown up under reading / live preview mode. Neither Properties UI, nor error hint (invalid frontmatter etc.)

Proposed solution

Either adding an empty properties UI, or providing error hint on empty object would be quite helpful. If the team wants to keep this behavior that’s also fine, I will adapt the plugin’s behavior.

The pitfall is, if the frontmatter content is left empty, user’s won’t get indicated, and would try to create another YAML block though this would fail, as the extra --- will only be recognized as a separator.