Discussed the issue during the Jan 30th WG call.

Conclusion is that Part 4 Table 135 DataValue clearly states a null shall be returned when StatusCode is BAD. "The data value. If the StatusCode indicates an error then the value is to be ignored and the Server shall set it to null."

The text in Part 4 "Part 4 states "If the Server has no known value - in particular when Severity is BAD, it shall return a NULL value." should be changed to remove the "if the Server has no known value - in particular when the Severity is BAD" to "When the Severity is BAD"

I think more discussion is needed on this ideally when Karl, Matthias, Jeff, Paul, Randy and I are present.

Here is my strawman for updates to Part 4:

https://opcfoundation.sharepoint.com/:w:/r/sites/wg.UA/Shared%20Documents/sg.Core/Meetings/2024/2024-01-30%20Weekly%20Web%20Meeting/OPC%2010000-4%20-%20UA%20Specification%20Part%204%20-%20Services%201.05.03%20Jim%20Luth%20Mantis%20%239372.docx

@Jim Luth
Your strawman includes this: "If a Variable is created and no default value or initial value is available, the StatusCode shall be Bad_NoValue."
Some use cases to consider:
1) Servers can have Variable Nodes with a non-NULL DataValue, which contain timestamps and a Good StatusCode, but a NULL value (this includes DataTypes other than String).
2) Servers can have Variable Nodes with a NULL DataValue, so it has no StatusCode (or timestamps, etc.).

Will the change to spec break existing Servers? What should the Client expect to get, and how should it interpret the return values?