diff --git a/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/AbstractFreeMarkerConfiguration.java b/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/AbstractFreeMarkerConfiguration.java
index cfb47f20acb..d0c9beff200 100644
--- a/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/AbstractFreeMarkerConfiguration.java
+++ b/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/AbstractFreeMarkerConfiguration.java
@@ -49,7 +49,10 @@ abstract class AbstractFreeMarkerConfiguration {
 	protected void applyProperties(FreeMarkerConfigurationFactory factory) {
 		factory.setTemplateLoaderPaths(this.properties.getTemplateLoaderPath());
 		factory.setPreferFileSystemAccess(this.properties.isPreferFileSystemAccess());
-		factory.setDefaultEncoding(this.properties.getCharsetName());
+		String charsetName = this.properties.getCharsetName();
+		if (charsetName != null) {
+			factory.setDefaultEncoding(charsetName);
+		}
 		factory.setFreemarkerSettings(createFreeMarkerSettings());
 		factory.setFreemarkerVariables(createFreeMarkerVariables());
 	}
diff --git a/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/FreeMarkerProperties.java b/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/FreeMarkerProperties.java
index 3dc7c27843a..150be308454 100644
--- a/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/FreeMarkerProperties.java
+++ b/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/FreeMarkerProperties.java
@@ -22,6 +22,8 @@ import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.Map;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.core.Ordered;
 import org.springframework.util.Assert;
@@ -71,7 +73,7 @@ public class FreeMarkerProperties {
 	/**
 	 * View names that can be resolved.
 	 */
-	private String[] viewNames;
+	private String @Nullable [] viewNames;
 
 	/**
 	 * Whether to check that the templates location exists.
@@ -91,7 +93,7 @@ public class FreeMarkerProperties {
 	/**
 	 * Name of the RequestContext attribute for all views.
 	 */
-	private String requestContextAttribute;
+	private @Nullable String requestContextAttribute;
 
 	/**
 	 * Whether all request attributes should be added to the model prior to merging with
@@ -157,11 +159,11 @@ public class FreeMarkerProperties {
 		return this.checkTemplateLocation;
 	}
 
-	public String[] getViewNames() {
+	public String @Nullable [] getViewNames() {
 		return this.viewNames;
 	}
 
-	public void setViewNames(String[] viewNames) {
+	public void setViewNames(String @Nullable [] viewNames) {
 		this.viewNames = viewNames;
 	}
 
@@ -191,7 +193,7 @@ public class FreeMarkerProperties {
 		return this.charset;
 	}
 
-	public String getCharsetName() {
+	public @Nullable String getCharsetName() {
 		return (this.charset != null) ? this.charset.name() : null;
 	}
 
@@ -239,11 +241,11 @@ public class FreeMarkerProperties {
 		this.suffix = suffix;
 	}
 
-	public String getRequestContextAttribute() {
+	public @Nullable String getRequestContextAttribute() {
 		return this.requestContextAttribute;
 	}
 
-	public void setRequestContextAttribute(String requestContextAttribute) {
+	public void setRequestContextAttribute(@Nullable String requestContextAttribute) {
 		this.requestContextAttribute = requestContextAttribute;
 	}
 
diff --git a/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/FreeMarkerTemplateAvailabilityProvider.java b/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/FreeMarkerTemplateAvailabilityProvider.java
index f6167d5f44b..f9f69a7440b 100644
--- a/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/FreeMarkerTemplateAvailabilityProvider.java
+++ b/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/FreeMarkerTemplateAvailabilityProvider.java
@@ -20,6 +20,8 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.aot.hint.RuntimeHints;
 import org.springframework.aot.hint.RuntimeHintsRegistrar;
 import org.springframework.boot.autoconfigure.template.PathBasedTemplateAvailabilityProvider;
@@ -69,7 +71,7 @@ public class FreeMarkerTemplateAvailabilityProvider extends PathBasedTemplateAva
 	static class FreeMarkerTemplateAvailabilityRuntimeHints implements RuntimeHintsRegistrar {
 
 		@Override
-		public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+		public void registerHints(RuntimeHints hints, @Nullable ClassLoader classLoader) {
 			if (ClassUtils.isPresent(REQUIRED_CLASS_NAME, classLoader)) {
 				BindableRuntimeHintsRegistrar.forTypes(FreeMarkerTemplateAvailabilityProperties.class)
 					.registerHints(hints, classLoader);
diff --git a/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/package-info.java b/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/package-info.java
index 0fa1da4d696..f17f5e4fd69 100644
--- a/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/package-info.java
+++ b/module/spring-boot-freemarker/src/main/java/org/springframework/boot/freemarker/autoconfigure/package-info.java
@@ -17,4 +17,7 @@
 /**
  * Auto-configuration for FreeMarker.
  */
+@NullMarked
 package org.springframework.boot.freemarker.autoconfigure;
+
+import org.jspecify.annotations.NullMarked;