Review fixes for nats-2.17:javaagent (#18219)

Co-authored-by: otelbot <197425009+otelbot@users.noreply.github.com>
Co-authored-by: Lauri Tulmin <ltulmin@splunk.com>

Author: otelbot[bot]

instrumentation/nats/nats-2.17/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/nats/v2_17/CompletableFutureWrapper.java

@@ -9,9 +9,7 @@
 import io.opentelemetry.context.Scope;
 import java.util.concurrent.CompletableFuture;
 
-public class CompletableFutureWrapper {
-
-  private CompletableFutureWrapper() {}
+class CompletableFutureWrapper {
 
   public static <T> CompletableFuture<T> wrap(CompletableFuture<T> future, Context context) {
     CompletableFuture<T> result = new CompletableFuture<>();
@@ -28,4 +26,6 @@ public static <T> CompletableFuture<T> wrap(CompletableFuture<T> future, Context
 
     return result;
   }
+
+  private CompletableFutureWrapper() {}
 }

instrumentation/nats/nats-2.17/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/nats/v2_17/MessageHandlerInstrumentation.java

@@ -48,7 +48,7 @@ public static class AdviceScope {
       private final Context context;
       private final Scope scope;
 
-      public AdviceScope(NatsRequest request, Context context, Scope scope) {
+      private AdviceScope(NatsRequest request, Context context, Scope scope) {
         this.request = request;
         this.context = context;
         this.scope = scope;
@@ -72,13 +72,15 @@ public void end(@Nullable Throwable throwable) {
     }
 
     @Advice.OnMethodEnter(suppress = Throwable.class, inline = false)
+    @Nullable
     public static AdviceScope onEnter(@Advice.Argument(0) Message message) {
       return AdviceScope.start(message);
     }
 
     @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class, inline = false)
     public static void onExit(
-        @Advice.Thrown @Nullable Throwable throwable, @Advice.Enter AdviceScope adviceScope) {
+        @Advice.Thrown @Nullable Throwable throwable,
+        @Advice.Enter @Nullable AdviceScope adviceScope) {
       if (adviceScope != null) {
         adviceScope.end(throwable);
       }

instrumentation/nats/nats-2.17/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/nats/v2_17/NatsSingletons.java

@@ -14,7 +14,7 @@
 import io.opentelemetry.javaagent.bootstrap.internal.ExperimentalConfig;
 import java.util.List;
 
-public class NatsSingletons {
+class NatsSingletons {
 
   private static final List<String> capturedHeaders =
       ExperimentalConfig.get().getMessagingHeaders();

instrumentation/nats/nats-2.17/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/nats/v2_17/SpanFinisher.java

@@ -12,7 +12,7 @@
 import io.opentelemetry.instrumentation.nats.v2_17.internal.NatsRequest;
 import java.util.function.BiConsumer;
 
-public class SpanFinisher implements BiConsumer<Message, Throwable> {
+class SpanFinisher implements BiConsumer<Message, Throwable> {
   private final Instrumenter<NatsRequest, NatsRequest> instrumenter;
   private final Context context;
   private final Connection connection;