Review fixes for akka-actor-2.3:javaagent (#16493)

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

Author: otelbot[bot]

instrumentation/akka/akka-actor-2.3/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/akkaactor/AkkaSchedulerTaskWrapper.java

@@ -6,10 +6,12 @@
 package io.opentelemetry.javaagent.instrumentation.akkaactor;
 
 import io.opentelemetry.context.Context;
+import javax.annotation.Nullable;
 
 public final class AkkaSchedulerTaskWrapper {
-  private static final Class<?> RUN_ON_CLOSE_TASK_CLASS = getRunOnCloseTaskClass();
+  @Nullable private static final Class<?> RUN_ON_CLOSE_TASK_CLASS = getRunOnCloseTaskClass();
 
+  @Nullable
   private static Class<?> getRunOnCloseTaskClass() {
     try {
       return Class.forName("akka.actor.Scheduler$TaskRunOnClose");