Use %ZEN.Auxiliary.JSONProvider class.

SQLCODE=100

would be a codepath for no data.

It's a valid sample. You just can't write directly into ZEN context. Well, you can, obviously, but that causes errors.

Where exactly in samples?

I'm not raising exceptions, but rather do logging. Here's the article.

Thank you! That's very useful.

Is there a way to return real implementation class?

For example, consider these classes:

Class App.Use {

ClassMethod Test()
{
    w 1/0
}
}

and:

Class App.Use2 Extends App.Use
{
}

If I call:

do ##class(App.Use2).Test()

I get  the following CLS source line:

App.Use2:Test+1

Yet, the relevant code is actually implemented in

App.Use:Test+1

One approach I see is checking %Dictionary.MethodDefinition recursively till I find a method definition, but there's bound to be many problems multiple inheritance.

You can set PasswordValidationRoutine in  the Security.System class. When a user is created in the Cache security database, or a user changes their password, the specified routine is called to validate the password. A tag reference may also be included in the property. The routine should be provided by the user, and must exist in the %SYS namespace (it may be mapped to a different database however.) The routine will take 2 parameters, a Username and new password, and should return a %Status code of $$$OK for successful password validation, or an error code formatted into a %Status variable. The username passed into the function will be in all lowercase, and will contain the domain name if multiple domains are enabled for the system.
 

Check out Cache-Fileserver.

Allowing client to specify server-side is not a recommended approach.

"C:\"_%request.MimeData("FileStream",1).FileName

Use incremented integers, hashes or guids instead.

Do you mean that you need to translate the data, rather than the metadata?

Here's an article on how to write your own zeppelin interpriner.