Review fixes for jms-common:bootstrap (open-telemetry#17462)

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

Author: otelbot[bot]

instrumentation/jms/jms-common/bootstrap/src/main/java/io/opentelemetry/javaagent/bootstrap/jms/JmsReceiveContextHolder.java

@@ -16,7 +16,7 @@ public final class JmsReceiveContextHolder implements ImplicitContextKeyed {
   private static final ContextKey<JmsReceiveContextHolder> KEY =
       named("opentelemetry-jms-receive-context");
 
-  private Context receiveContext;
+  @Nullable private Context receiveContext;
 
   private JmsReceiveContextHolder() {}