polish debug logging avoid null value when segment be ignored. (#7070)

* polish debug logging avoid null value.

* update CHANGES.md.

CHANGES.md

@@ -61,6 +61,7 @@ Release Notes.
 * Make metrics exporter still work even when storage layer failed.
 * Fix Jetty HTTP `TRACE` issue, disable HTTP methods except `POST`.
 * CVE: upgrade snakeyaml to prevent [billion laughs attack](https://en.wikipedia.org/wiki/Billion_laughs#Variations) in dynamic configuration.
+* polish debug logging avoids null value when the segment ignored.
 
 #### UI
 * Add logo for kong plugin.

oap-server/analyzer/agent-analyzer/src/main/java/org/apache/skywalking/oap/server/analyzer/provider/trace/parser/listener/SegmentAnalysisListener.java

@@ -170,14 +170,17 @@ public class SegmentAnalysisListener implements FirstAnalysisListener, EntryAnal
 
     @Override
     public void build() {
-        if (log.isDebugEnabled()) {
-            log.debug("segment listener build, segment id: {}", segment.getSegmentId());
-        }
-
         if (sampleStatus.equals(SAMPLE_STATUS.IGNORE)) {
+            if (log.isDebugEnabled()) {
+                log.debug("segment ignored, trace id: {}", segment.getTraceId());
+            }
             return;
         }
 
+        if (log.isDebugEnabled()) {
+            log.debug("segment listener build, segment id: {}", segment.getSegmentId());
+        }
+
         segment.setEndpointId(endpointId);
         segment.setEndpointName(endpointName);