[Bug] 2.70.1 causes random NullReferenceException failures with custom templates.

[esbenk]

Describe the bug
When building sites with custom templates the 2.70.1 version causes random errors. I'm testing on a project with ~8000 yaml files with our own template (Doc support for https://marketplace.visualstudio.com/items?itemName=ms-dynamics-smb.al). On average 1/3 of the yaml files fails with

C:\src\aldoc\docs\reference\base-application\Page\Microsoft.InventoryMgt.Ledger.Value-Entries-Preview.yml: error InvalidInputFile: Unable to load file 'reference/base-application/Page/Microsoft.InventoryMgt.Ledger.Value-Entries-Preview.yml' via processor 'BusinessCentralApplicationObject': Object reference not set to an instance of an object.

The exception happens when trying to validate the yaml against the BusinessCentralObject schema. The exceptions is thrown in this line

https://github.com/dotnet/docfx/blob/5e266b2621c92b5ef5193ac69db4bfe73e486030/src/Docfx.Build.SchemaDriven/Validators/SchemaValidator.cs#L28C20-L28C20

It is caused by the update of JsonSchema.Net to version 5.00 in this PR #9041.

Reverting to version 4.1.8 solves the issue.

It is probably related to this bug in JsonSchema.Net:

json-everything/json-everything#502

To Reproduce
Steps to reproduce the behavior:

1. Use custom template with schema.
2. Build the project. If the project contains many files it will fail every time, smaller project build a couple of times.

Expected behavior
No random NullReferences when using custom templates.

Context (please complete the following information):

• OS: Windows 11
• Docfx version: [e.g. 2.70.1]

Additional context
Add any other context about the problem here.

[gregsdennis]

Hello.

So while investigating ☝️ I found an issue with your meta-schema. Primarily, JSON Schema draft 6 uses $id (with a $) not id as its identifying keyword. This is a change from draft 4, and I suspect it's likely a typo during any conversion that may have occurred. As it is, id is just skipped as an unknown keyword. This is not new behavior.

I'd still like to get an actual minimal reproduction of this bug. My analysis (of my code) indicates that the variable in that code should never be null, which means something before that is wrong. The exception that's actually thrown doesn't help me as literally every keyword generates a KeywordEvaluation object.

Also, I'm not sure why:

• you've written your meta-schema as draft 6, but you're using draft 7 on this line
• you've decided to re-register draft 7 under a new URI

[gregsdennis]

Upcoming JsonSchema.Net v5.2.5 (now published) should fix the issue.

Would still be good to address the issues above.

[yufeih]

Thank you @gregsdennis ! I updated the problems with meta schema according to your findings.