Minor improvements to shallow trace

Author: cpettitt-linkedin

src/com/linkedin/parseq/trace/ShallowTrace.java

@@ -65,8 +65,15 @@ public class ShallowTrace
     _endNanos = endNanos;
     _systemHidden = systemHidden;
 
-    Map<String, String> attributeMap = new HashMap<String, String>(attributes);
-    _attributes = Collections.unmodifiableMap(attributeMap);
+    if (!attributes.isEmpty())
+    {
+      Map<String, String> attributeMap = new HashMap<String, String>(attributes);
+      _attributes = Collections.unmodifiableMap(attributeMap);
+    }
+    else
+    {
+      _attributes = Collections.emptyMap();
+    }
 
     switch (resultType)
     {

src/com/linkedin/parseq/trace/ShallowTraceBuilder.java

@@ -19,7 +19,6 @@
 import com.linkedin.parseq.internal.ArgumentUtil;
 
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 
@@ -41,7 +40,7 @@ public class ShallowTraceBuilder
   private volatile Long _pendingNanos;
   private volatile Long _endNanos;
   private volatile boolean _systemHidden;
-  private final Map<String,String> _attributes;
+  private final Map<String,String> _attributes = new ConcurrentHashMap<String, String>();
 
   public ShallowTraceBuilder(final ShallowTrace shallowTrace)
   {
@@ -69,7 +68,6 @@ public ShallowTraceBuilder(String name, ResultType resultType)
   public ShallowTraceBuilder(ResultType resultType)
   {
     setResultType(resultType);
-    _attributes = new ConcurrentHashMap<String, String>();
   }
 
   public boolean getHidden()