diff --git a/spring-kafka-docs/build.gradle b/spring-kafka-docs/build.gradle
index 4dc44df36f..103805238a 100644
--- a/spring-kafka-docs/build.gradle
+++ b/spring-kafka-docs/build.gradle
@@ -7,7 +7,6 @@ apply from: "${rootDir}/gradle/docs.gradle"
 apply plugin: 'java'
 apply plugin: 'eclipse'
 apply plugin: 'idea'
-apply plugin: 'checkstyle'
 apply plugin: 'kotlin'
 apply plugin: 'kotlin-spring'
 
diff --git a/spring-kafka-docs/src/main/kotlin/org/springframework/kafka/kdocs/dynamic/Application.kt b/spring-kafka-docs/src/main/kotlin/org/springframework/kafka/kdocs/dynamic/Application.kt
index 6350987ee0..fba0d96111 100644
--- a/spring-kafka-docs/src/main/kotlin/org/springframework/kafka/kdocs/dynamic/Application.kt
+++ b/spring-kafka-docs/src/main/kotlin/org/springframework/kafka/kdocs/dynamic/Application.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 the original author or authors.
+ * Copyright 2022-2023 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.
@@ -39,12 +39,12 @@ import org.springframework.kafka.listener.MessageListener
 class Application {
     @Bean
     fun runner(factory: ConcurrentKafkaListenerContainerFactory<String, String>): ApplicationRunner {
-        return ApplicationRunner { args: ApplicationArguments? -> createContainer(factory, "topic1", "group1") }
+        return ApplicationRunner { _ : ApplicationArguments? -> createContainer(factory, "topic1", "group1") }
     }
 
     @Bean
     fun runner(applicationContext: ApplicationContext): ApplicationRunner {
-        return ApplicationRunner { args: ApplicationArguments? ->
+        return ApplicationRunner { _: ApplicationArguments? ->
 // tag::getBeans[]
 
 applicationContext.getBean(MyPojo::class.java, "one", arrayOf("topic2"))
diff --git a/spring-kafka-docs/src/main/kotlin/org/springframework/kafka/kdocs/requestreply/Application.kt b/spring-kafka-docs/src/main/kotlin/org/springframework/kafka/kdocs/requestreply/Application.kt
index 486abd9165..b7781dd58b 100644
--- a/spring-kafka-docs/src/main/kotlin/org/springframework/kafka/kdocs/requestreply/Application.kt
+++ b/spring-kafka-docs/src/main/kotlin/org/springframework/kafka/kdocs/requestreply/Application.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2021 the original author or authors.
+ * Copyright 2021-2023 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.
@@ -112,7 +112,7 @@ class Application {
         }
         return if (`in` == "\"getThings\"") {
             "[{\"thingProp\":\"someValue1\"},{\"thingProp\":\"someValue2\"}]".toByteArray()
-        } else `in`.toUpperCase().toByteArray()
+        } else `in`.uppercase().toByteArray()
     }
 
     class Thing {
diff --git a/spring-kafka/src/test/java/org/springframework/kafka/support/transaction/ResourcelessTransactionManager.java b/spring-kafka/src/test/java/org/springframework/kafka/support/transaction/ResourcelessTransactionManager.java
index c89996f9fa..f411387744 100644
--- a/spring-kafka/src/test/java/org/springframework/kafka/support/transaction/ResourcelessTransactionManager.java
+++ b/spring-kafka/src/test/java/org/springframework/kafka/support/transaction/ResourcelessTransactionManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2020 the original author or authors.
+ * Copyright 2017-2023 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.
@@ -85,7 +85,7 @@ protected void doCleanupAfterCompletion(Object transaction) {
 		((ResourcelessTransaction) transaction).clear();
 	}
 
-	private static class ResourcelessTransaction {
+	private static final class ResourcelessTransaction {
 
 		private boolean active = false;