Remove jackson-module-kotlin warning

Closes gh-26962

Author: sdeleuze

spring-web/src/main/java/org/springframework/http/converter/json/Jackson2ObjectMapperBuilder.java

@@ -105,8 +105,6 @@
  */
 public class Jackson2ObjectMapperBuilder {
 
-	private static volatile boolean kotlinWarningLogged;
-
 	private final Log logger = HttpLogging.forLogName(getClass());
 
 	private final Map<Class<?>, Class<?>> mixIns = new LinkedHashMap<>();
@@ -863,11 +861,7 @@ private void registerWellKnownModulesIfAvailable(MultiValueMap<Object, Module> m
 				modulesToRegister.set(kotlinModule.getTypeId(), kotlinModule);
 			}
 			catch (ClassNotFoundException ex) {
-				if (!kotlinWarningLogged) {
-					kotlinWarningLogged = true;
-					logger.warn("For Jackson Kotlin classes support please add " +
-							"\"com.fasterxml.jackson.module:jackson-module-kotlin\" to the classpath");
-				}
+				// jackson-module-kotlin not available
 			}
 		}
 	}

src/docs/asciidoc/languages/kotlin.adoc

@@ -31,6 +31,11 @@ and https://bintray.com/bintray/jcenter/org.jetbrains.kotlin%3Akotlin-reflect[`k
 to be present on the classpath. They are provided by default if you bootstrap a Kotlin project on
 https://start.spring.io/#!language=kotlin&type=gradle-project[start.spring.io].
 
+NOTE: The https://github.com/FasterXML/jackson-module-kotlin[Jackson Kotlin module] is required
+for serializing or deserializing JSON data for Kotlin classes with Jackson, so make sure to add the
+`com.fasterxml.jackson.module:jackson-module-kotlin` dependency to your project if you have such need.
+It is automatically registered when found in the classpath.
+
 [[kotlin-extensions]]
 == Extensions
 
@@ -120,11 +125,6 @@ Kotlin parameter names are recognized through a dedicated `KotlinReflectionParam
 which allows finding interface method parameter names without requiring the Java 8 `-parameters`
 compiler flag to be enabled during compilation.
 
-The https://github.com/FasterXML/jackson-module-kotlin[Jackson Kotlin module], which is required
-for serializing or deserializing JSON data, is automatically registered when
-found in the classpath, and a warning message is logged if Jackson and Kotlin are
-detected without the Jackson Kotlin module being present.
-
 You can declare configuration classes as
 https://kotlinlang.org/docs/reference/nested-classes.html[top level or nested but not inner],
 since the later requires a reference to the outer class.