Add checkstyle rule on empty-line-separater

* Update checkstyle.xml
* Fix checkstyle violations
* Fix test class checkstyle
* Add field also.

Author: JooHyukKim

spring-kafka-test/src/main/java/org/springframework/kafka/test/EmbeddedKafkaKraftBroker.java

@@ -204,7 +204,6 @@ public void afterPropertiesSet() {
 		}
 	}
 
-
 	private void start() {
 		if (this.cluster != null) {
 			return;

spring-kafka-test/src/main/java/org/springframework/kafka/test/assertj/KafkaConditions.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -90,7 +90,6 @@ public static <K, V> Condition<ConsumerRecord<K, V>> keyValue(K key, V value) {
 		return new ConsumerRecordPartitionCondition(partition);
 	}
 
-
 	public static class ConsumerRecordKeyCondition<K> extends Condition<ConsumerRecord<K, ?>> {
 
 		private final K key;

spring-kafka-test/src/main/java/org/springframework/kafka/test/condition/EmbeddedKafkaCondition.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2019-2023 the original author or authors.
+ * Copyright 2019-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -211,7 +211,6 @@ private Store getParentStore(ExtensionContext context) {
 		return parent.getStore(Namespace.create(getClass(), parent));
 	}
 
-
 	public static EmbeddedKafkaBroker getBroker() {
 		return BROKERS.get();
 	}

spring-kafka-test/src/test/java/org/springframework/kafka/test/context/EmbeddedKafkaContextCustomizerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2023 the original author or authors.
+ * Copyright 2017-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,15 +48,13 @@ void beforeEachTest() {
 				AnnotationUtils.findAnnotation(SecondTestWithEmbeddedKafka.class, EmbeddedKafka.class);
 	}
 
-
 	@Test
 	void testHashCode() {
 		assertThat(new EmbeddedKafkaContextCustomizer(annotationFromFirstClass).hashCode()).isNotEqualTo(0);
 		assertThat(new EmbeddedKafkaContextCustomizer(annotationFromFirstClass).hashCode())
 				.isEqualTo(new EmbeddedKafkaContextCustomizer(annotationFromSecondClass).hashCode());
 	}
 
-
 	@Test
 	void testEquals() {
 		assertThat(new EmbeddedKafkaContextCustomizer(annotationFromFirstClass))
@@ -93,7 +91,6 @@ void testMulti() {
 				.matches("127.0.0.1:[0-9]+,127.0.0.1:[0-9]+");
 	}
 
-
 	@EmbeddedKafka(kraft = false)
 	private static final class TestWithEmbeddedKafka {
 

spring-kafka/src/main/java/org/springframework/kafka/annotation/KafkaListenerAnnotationBeanPostProcessor.java

@@ -1190,7 +1190,6 @@ private MessageHandlerMethodFactory createDefaultMessageHandlerMethodFactory() {
 
 	private record BytesToStringConverter(Charset charset) implements Converter<byte[], String> {
 
-
 		@Override
 		public String convert(byte[] source) {
 			return new String(source, this.charset);

spring-kafka/src/main/java/org/springframework/kafka/annotation/RetryTopicConfigurationProvider.java

@@ -37,7 +37,6 @@
 import org.springframework.kafka.retrytopic.RetryTopicConfiguration;
 import org.springframework.lang.Nullable;
 
-
 /**
  *
  * Attempts to provide an instance of

spring-kafka/src/main/java/org/springframework/kafka/config/KafkaListenerEndpointRegistry.java

@@ -361,7 +361,6 @@ else if (endpoint instanceof MethodKafkaListenerEndpoint<?, ?> mkle) {
 		return listenerContainer;
 	}
 
-
 	@Override
 	public void destroy() {
 		for (MessageListenerContainer listenerContainer : getListenerContainers()) {
@@ -419,7 +418,6 @@ public boolean isRunning() {
 		return this.running;
 	}
 
-
 	@Override
 	public void onApplicationEvent(ContextRefreshedEvent event) {
 		if (event.getApplicationContext().equals(this.applicationContext)) {
@@ -439,7 +437,6 @@ private void startIfNecessary(MessageListenerContainer listenerContainer) {
 		}
 	}
 
-
 	private static final class AggregatingCallback implements Runnable {
 
 		private final AtomicInteger count;

spring-kafka/src/main/java/org/springframework/kafka/config/MultiMethodKafkaListenerEndpoint.java

@@ -61,7 +61,6 @@ public MultiMethodKafkaListenerEndpoint(List<Method> methods, @Nullable Method d
 		setBean(bean);
 	}
 
-
 	/**
 	 * Get a method list.
 	 * @return the method list.

spring-kafka/src/main/java/org/springframework/kafka/core/DefaultKafkaConsumerFactory.java

@@ -252,7 +252,6 @@ public void setValueDeserializerSupplier(Supplier<Deserializer<V>> valueDeserial
 		this.valueDeserializerSupplier = valueDeserializerSupplier(valueDeserializerSupplier);
 	}
 
-
 	/**
 	 * Set to false (default true) to prevent programmatically provided deserializers (via
 	 * constructor or setters) from being configured using the producer configuration,

spring-kafka/src/main/java/org/springframework/kafka/core/DefaultKafkaProducerFactory.java

@@ -68,8 +68,6 @@
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
-
-
 /**
  * The {@link ProducerFactory} implementation for a {@code singleton} shared {@link Producer} instance.
  * <p>
@@ -567,7 +565,6 @@ public ProducerFactory<K, V> copyWithConfigurationOverride(Map<String, Object> o
 		return newFactory;
 	}
 
-
 	/**
 	 * Ensures that the returned properties map contains a transaction id prefix.
 	 * The {@link org.springframework.kafka.core.DefaultKafkaProducerFactory}