Move to new API because of deprecation and add correct annotation

src/main/java/de/thm/arsnova/websocket/handler/AuthChannelInterceptorAdapter.java

@@ -5,7 +5,6 @@ import org.checkerframework.checker.nullness.qual.Nullable;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.lang.NonNull;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.messaging.simp.stomp.StompCommand;
@@ -31,7 +30,7 @@ public class AuthChannelInterceptorAdapter implements ChannelInterceptor {
 
 	@Nullable
 	@Override
-	public Message<?> preSend(@NonNull final Message<?> message, final MessageChannel channel) {
+	public Message<?> preSend(final Message<?> message, final MessageChannel channel) {
 		logger.trace("Inspecting incoming message: {}", message);
 		final StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);