Do not create a baggage HashMap each time

dd-trace/src/main/java/com/datadoghq/trace/DDSpanContext.java

@@ -1,18 +1,13 @@
 package com.datadoghq.trace;
 
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-
 import com.datadoghq.trace.integration.DDSpanContextDecorator;
 import com.fasterxml.jackson.annotation.JsonIgnore;
-
 import io.opentracing.Span;
 import io.opentracing.tag.Tags;
 
+import java.util.*;
+
 /**
  * SpanContext represents Span state that must propagate to descendant Spans and across process boundaries.
  * <p>
@@ -81,8 +76,9 @@ public class DDSpanContext implements io.opentracing.SpanContext {
 		this.spanId = spanId;
 		this.parentId = parentId;
 
+
 		if (baggageItems == null) {
-			this.baggageItems = new HashMap<String, String>();
+			this.baggageItems = Collections.emptyMap();
 		} else {
 			this.baggageItems = baggageItems;
 		}
@@ -134,6 +130,9 @@ public class DDSpanContext implements io.opentracing.SpanContext {
 	}
 
 	public void setBaggageItem(String key, String value) {
+		if (this.baggageItems.isEmpty()) {
+			this.baggageItems = new HashMap<String, String>();
+		}
 		this.baggageItems.put(key, value);
 	}
 

dd-trace/src/main/java/com/datadoghq/trace/DDTracer.java

@@ -304,7 +304,7 @@ public class DDTracer implements io.opentracing.Tracer {
                     serviceName,
                     operationName,
                     this.resourceName,
-                    this.parent == null ? new HashMap<String, String>() : p.getBaggageItems(),
+                    this.parent == null ? null : p.getBaggageItems(),
                     errorFlag,
                     spanType,
                     this.tags,