Use singleton for null telemetry objects in NullTelemetryFactory (#1188)

Author: johnou

wrapper/src/main/java/software/amazon/jdbc/util/telemetry/NullTelemetryFactory.java

@@ -18,9 +18,13 @@
 
 public class NullTelemetryFactory implements TelemetryFactory {
 
+  private static final TelemetryContext NULL_TELEMETRY_CONTEXT = new NullTelemetryContext("null");
+  private static final TelemetryCounter NULL_TELEMETRY_COUNTER = new NullTelemetryCounter("null");
+  private static final TelemetryGauge NULL_TELEMETRY_GAUGE = new NullTelemetryGauge("null");
+
   @Override
   public TelemetryContext openTelemetryContext(String name, TelemetryTraceLevel traceLevel) {
-    return new NullTelemetryContext(name);
+    return NULL_TELEMETRY_CONTEXT;
   }
 
   @Override
@@ -30,11 +34,11 @@ public void postCopy(TelemetryContext telemetryContext, TelemetryTraceLevel trac
 
   @Override
   public TelemetryCounter createCounter(String name) {
-    return new NullTelemetryCounter(name);
+    return NULL_TELEMETRY_COUNTER;
   }
 
   @Override
   public TelemetryGauge createGauge(String name, GaugeCallable<Long> callback) {
-    return new NullTelemetryGauge(name);
+    return NULL_TELEMETRY_GAUGE;
   }
 }