Don't clear Preview when Response Filter is invalid/non-existent

[yozlet]

Following on from #1258:

Short version: Only update the Response Preview when the Response Filter evaluation returns something worth showing.

In more detail:

• Given: the Preview pane is displaying any response content
• When: the Response Filter input changes
• And: the Response Filter input evaluates as either syntactically invalid or non-existent in the current document
• Then: don't update the Preview to show [] or similar, as it hides the document tree that the user is currently trying to navigate.

Example: If I'm trying to filter down to $.store.books[*].author, then as soon as I type $. the Preview just shows [], and I won't see anything useful until I either delete or type as far as $.store . This is particularly annoying if I'm continually looking at the Preview as a guide to the path I'm typing.

[gschier]

Hmm, I think the suggestion could possibly be confusing as well in the current state, but would probably be fine if #1258 were first implemented. That way the user would still see visual feedback, even though the editor contents did not change.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[yozlet]

@gschier Can this one be reopened? Sure, it's been a long time, but it's still a valid enhancement.

[gschier]

Yep, sorry. Have been having some trouble with stalebot lately