StdDelegatingDeserializer ignores nullValue of _delegateDeserializer.

[k163377]

Describe the bug
StdDelegatingDeserializer does not properly override methods such as getNullValue.
This prevents Converter from working when the value is null.

Version information
2.14.1

To Reproduce
I think I can read it from the source code, but I will write it if necessary.
https://github.com/FasterXML/jackson-databind/blob/ae3ca887c589e075ed13ea0665ac9bf22c0517a9/src/main/java/com/fasterxml/jackson/databind/deser/std/StdDelegatingDeserializer.java

Expected behavior
override a method such as getNullValue and call Converter if the result of such a method call to _delegateDeserializer is not null.

Additional context
There was a situation where the value class deserialization in jackson-module-kogera needed to be enabled.
https://github.com/ProjectMapK/jackson-module-kogera

[cowtowncoder]

@k163377 yes, I think you are right wrt delegation, methods are missing. And I suppose calling of Converter makes sense as well. There are a few other methods missing too so it'd make sense to address those as well.

I think this would qualify to be in 2.14(.2).

I can probably work on this, time permitting, to get it in 2.14.2. Or if you want to do PR, happy to review. Methods from JsonSerializer that seem to be missing:

• isCachable
• getKnownPropertyNames
• unwrappingDeserializer (may need to re-construct delegating one itself)
• replaceDelegatee (not sure this is actually used anywhere but...)
• getNullValue / getNullAccessPattern
• getAbsentValue
• getEmptyValue / getEmptyAccessPattern
• getObjectIdReader
• findBackReference

So I think all of those should delegate. Although one way to reduce risk would be to only delegate getXxxValue()/getXxxAccessPattern() calls for 2.14(.2), and the rest in 2.15.
Although I am not sure why delegation should break anything it might still be safest.

Ideally we'd also have unit tests for these which adds to work.

[cowtowncoder]

Actually, I think overrides may or may not make sense so need to check on case by case basis: pure delegating only via DelegatingDeserializer: StdDelegatingDeserializer should really be called [Std]ConvertingDeserializer instead due to conversion step. This conversion step also means that some delegation may either not make sense or cannot be handled in general manner.

EDIT: and in fact 3.0 does that.