Added header null check and changelog

Signed-off-by: Nishchay Malhotra <nishcha@amazon.com>

CHANGELOG.md

@@ -116,6 +116,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Make search query counters dynamic to support all query types ([#12601](https://github.com/opensearch-project/OpenSearch/pull/12601))
 - [Tiered caching] Add policies controlling which values can enter pluggable caches [EXPERIMENTAL] ([#12542](https://github.com/opensearch-project/OpenSearch/pull/12542))
 - [Tiered caching] Add Stale keys Management and CacheCleaner to IndicesRequestCache ([#12625](https://github.com/opensearch-project/OpenSearch/pull/12625))
+- [Tracing Framework] Adds support for inferred sampling ([#12315](https://github.com/opensearch-project/OpenSearch/issues/12315))
 
 ### Dependencies
 - Bump `peter-evans/find-comment` from 2 to 3 ([#12288](https://github.com/opensearch-project/OpenSearch/pull/12288))

libs/telemetry/src/main/java/org/opensearch/telemetry/tracing/DefaultTracer.java

@@ -109,7 +109,7 @@ public Span startSpan(SpanCreationContext spanCreationContext, Map<String, Colle
     }
 
     private void addRequestAttributeToContext(SpanCreationContext spanCreationContext, Map<String, Collection<String>> headers) {
-        if (headers.containsKey(TracerContextStorage.INFERRED_SAMPLER)) {
+        if (headers !=null && headers.containsKey(TracerContextStorage.INFERRED_SAMPLER)) {
             spanCreationContext.getAttributes().addAttribute(TracerContextStorage.INFERRED_SAMPLER, true);
         }
     }