Review fixes for async-http-client-2.0:javaagent (open-telemetry#17266)

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

Author: otelbot[bot]

instrumentation/async-http-client/async-http-client-2.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/asynchttpclient/v2_0/AsyncCompletionHandlerInstrumentation.java

@@ -16,6 +16,7 @@
 import io.opentelemetry.context.Scope;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeTransformer;
+import javax.annotation.Nullable;
 import net.bytebuddy.asm.Advice;
 import net.bytebuddy.description.type.TypeDescription;
 import net.bytebuddy.matcher.ElementMatcher;
@@ -49,6 +50,7 @@ public void transform(TypeTransformer transformer) {
   @SuppressWarnings("unused")
   public static class OnCompletedAdvice {
 
+    @Nullable
     @Advice.OnMethodEnter(suppress = Throwable.class)
     public static Scope onEnter(
         @Advice.This AsyncCompletionHandler<?> handler, @Advice.Argument(0) Response response) {
@@ -63,7 +65,7 @@ public static Scope onEnter(
     }
 
     @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)
-    public static void onExit(@Advice.Enter Scope scope) {
+    public static void onExit(@Advice.Enter @Nullable Scope scope) {
       if (null != scope) {
         scope.close();
       }
@@ -73,6 +75,7 @@ public static void onExit(@Advice.Enter Scope scope) {
   @SuppressWarnings("unused")
   public static class OnThrowableAdvice {
 
+    @Nullable
     @Advice.OnMethodEnter(suppress = Throwable.class)
     public static Scope onEnter(
         @Advice.This AsyncCompletionHandler<?> handler, @Advice.Argument(0) Throwable throwable) {
@@ -87,7 +90,7 @@ public static Scope onEnter(
     }
 
     @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)
-    public static void onExit(@Advice.Enter Scope scope) {
+    public static void onExit(@Advice.Enter @Nullable Scope scope) {
       if (null != scope) {
         scope.close();
       }

instrumentation/async-http-client/async-http-client-2.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/asynchttpclient/v2_0/AsyncHttpClientSingletons.java

@@ -16,12 +16,12 @@
 public final class AsyncHttpClientSingletons {
   private static final String INSTRUMENTATION_NAME = "io.opentelemetry.async-http-client-2.0";
 
-  private static final Instrumenter<RequestContext, Response> INSTRUMENTER;
+  private static final Instrumenter<RequestContext, Response> instrumenter;
   public static final VirtualField<AsyncHandler<?>, RequestContext> ASYNC_HANDLER_REQUEST_CONTEXT;
   public static final VirtualField<Request, Context> REQUEST_CONTEXT;
 
   static {
-    INSTRUMENTER =
+    instrumenter =
         JavaagentHttpClientInstrumenters.create(
             INSTRUMENTATION_NAME,
             new AsyncHttpClientHttpAttributesGetter(),
@@ -32,7 +32,7 @@ public final class AsyncHttpClientSingletons {
   }
 
   public static Instrumenter<RequestContext, Response> instrumenter() {
-    return INSTRUMENTER;
+    return instrumenter;
   }
 
   private AsyncHttpClientSingletons() {}

instrumentation/async-http-client/async-http-client-2.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/asynchttpclient/v2_0/NettyRequestSenderInstrumentation.java

@@ -17,6 +17,7 @@
 import io.opentelemetry.javaagent.bootstrap.Java8BytecodeBridge;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeTransformer;
+import javax.annotation.Nullable;
 import net.bytebuddy.asm.Advice;
 import net.bytebuddy.description.type.TypeDescription;
 import net.bytebuddy.matcher.ElementMatcher;
@@ -66,6 +67,7 @@ public static void attachContext(@Advice.Argument(0) Request request) {
   @SuppressWarnings("unused")
   public static class MountContextAdvice {
 
+    @Nullable
     @Advice.OnMethodEnter(suppress = Throwable.class)
     public static Scope mountContext(@Advice.Argument(0) NettyResponseFuture<?> responseFuture) {
       Request request = responseFuture.getCurrentRequest();
@@ -74,7 +76,7 @@ public static Scope mountContext(@Advice.Argument(0) NettyResponseFuture<?> resp
     }
 
     @Advice.OnMethodExit(onThrowable = Throwable.class, suppress = Throwable.class)
-    public static void unmountContext(@Advice.Enter Scope scope) {
+    public static void unmountContext(@Advice.Enter @Nullable Scope scope) {
       if (scope != null) {
         scope.close();
       }