Database Sampling not working for JSON

[josvanroosmalen]

Several MLCS people reported that JSON Database sampling is not working. I have analysed this issue, and I am working on a fix.

[markschiffner]

I created a gradle task to load the farmers data as json. When I try to create a query, I get a UI error "Server Error. Please try again later." when trying to save the query.
Steps to reproduce:

1. Load the farmers data: gradle loadDemoDataJSON
2. Edit Config, Create a query
3. Sample the database, choose JSON
4. Choose Data-Explorer-content; should have 8,675 json documents
5. Set collections to JSONDemoData, hit enter, not sure if the lookup button does anything.
6. Choose document type "/" - Not sure what this means in context of JSON, could be the issue?
7. Press select fields button
8. Enter query name
9. Path filter is a issue!!! We don't see, to have a "root" json choice - Choose /MarketPlace
10. Set MarketName to Both and save -- Gets the error!!!

Issues:

1. The error upon saving
2. Having the path filter that does not have root, seems like it will use / on the screen, but not the choose relevant fields page.
3. On pick a Document Type, does Lookup button do anything?