fix: return empty PAnnotationValue for NullAnnotation to prevent NPE

[waterWang]

Fixes #14127

Problem

AnnotationValueMapper.map(Annotation<?>) returns null when the annotation is a NullAnnotation. The caller (SpanMessageMapper.map(Annotation<?>) → PAnnotation.Builder.setValue(...)) does not guard against a null return value, causing a NullPointerException:

PAnnotation.Builder.setValue(null)  ← NullPointerException

This causes span data loss, for example when ES version information cannot be collected.

Root cause

The NullAnnotation class was designed to represent annotations with a null value, but the mapper's NullAnnotation branch returns null instead of a valid empty PAnnotationValue. The calling code in SpanMessageMapper unconditionally calls pAnnotation.setValue(annotationValueMapper.map(annotation)) without a null check.

Fix

Return an empty PAnnotationValue (via getAnnotationBuilder().build()) instead of null when the annotation is a NullAnnotation. This preserves the semantics of "no annotation value" while preventing the NPE in the caller.

 default PAnnotationValue map(Annotation<?> annotation) {
     if (annotation instanceof NullAnnotation) {
-        return null;
+        return getAnnotationBuilder().build();
     }
     return mapNonNull(annotation);
 }

Impact

The NPE has a high impact — it causes span data loss. The fix is minimal and safe: returning an empty PAnnotationValue is equivalent to the previous behavior of returning null from the caller's perspective (the builder accepts an empty value), but avoids the crash.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud