diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SanitizableData.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SanitizableData.java
index eecf7f7ee00..1481a9c9e06 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SanitizableData.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SanitizableData.java
@@ -21,6 +21,7 @@ import java.util.Locale;
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.env.PropertySource;
+import org.springframework.util.Assert;
 
 /**
  * Value object that represents the data that can be used by a {@link SanitizingFunction}.
@@ -38,7 +39,7 @@ public final class SanitizableData {
 
 	private final @Nullable PropertySource<?> propertySource;
 
-	private final @Nullable String key;
+	private final String key;
 
 	private @Nullable String lowerCaseKey;
 
@@ -50,7 +51,8 @@ public final class SanitizableData {
 	 * @param key the data key
 	 * @param value the data value
 	 */
-	public SanitizableData(@Nullable PropertySource<?> propertySource, @Nullable String key, @Nullable Object value) {
+	public SanitizableData(@Nullable PropertySource<?> propertySource, String key, @Nullable Object value) {
+		Assert.notNull(key, "'key' must not be null");
 		this.propertySource = propertySource;
 		this.key = key;
 		this.value = value;
@@ -69,7 +71,7 @@ public final class SanitizableData {
 	 * Return the key of the data.
 	 * @return the data key
 	 */
-	public @Nullable String getKey() {
+	public String getKey() {
 		return this.key;
 	}
 
@@ -78,9 +80,9 @@ public final class SanitizableData {
 	 * @return the key as a lowercase value
 	 * @since 3.5.0
 	 */
-	public @Nullable String getLowerCaseKey() {
+	public String getLowerCaseKey() {
 		String result = this.lowerCaseKey;
-		if (result == null && this.key != null) {
+		if (result == null) {
 			result = this.key.toLowerCase(Locale.getDefault());
 			this.lowerCaseKey = result;
 		}
diff --git a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SanitizingFunction.java b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SanitizingFunction.java
index 89f1a5e47ef..2c140c3e43a 100644
--- a/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SanitizingFunction.java
+++ b/module/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SanitizingFunction.java
@@ -399,13 +399,12 @@ public interface SanitizingFunction {
 		Assert.notNull(predicate, "'predicate' must not be null");
 		Assert.notNull(value, "'value' must not be null");
 		String lowerCaseValue = value.toLowerCase(Locale.getDefault());
-		return (data) -> nullSafeTest(data.getLowerCaseKey(),
-				(lowerCaseKey) -> predicate.test(lowerCaseKey, lowerCaseValue));
+		return (data) -> predicate.test(data.getLowerCaseKey(), lowerCaseValue);
 	}
 
 	private Predicate<SanitizableData> onKey(Predicate<String> predicate) {
 		Assert.notNull(predicate, "'predicate' must not be null");
-		return (data) -> nullSafeTest(data.getKey(), predicate);
+		return (data) -> predicate.test(data.getKey());
 	}
 
 	private Predicate<SanitizableData> onValue(Predicate<Object> predicate) {
diff --git a/module/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/SanitizingFunctionTests.java b/module/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/SanitizingFunctionTests.java
index 03b4e5fe847..2ac5b39625c 100644
--- a/module/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/SanitizingFunctionTests.java
+++ b/module/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/SanitizingFunctionTests.java
@@ -136,7 +136,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToKey(function, "boot").has(unsanitizedValue());
 		assertThatApplyingToKey(function, "xspring").has(unsanitizedValue());
 		assertThatApplyingToKey(function, "springx").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -148,7 +147,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToKey(function, "boot").has(sanitizedValue());
 		assertThatApplyingToKey(function, "atest").has(sanitizedValue());
 		assertThatApplyingToKey(function, "bootx").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -160,7 +158,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToKey(function, "boot").has(sanitizedValue());
 		assertThatApplyingToKey(function, "beet").has(sanitizedValue());
 		assertThatApplyingToKey(function, "spring").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -171,7 +168,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToKey(function, "XtestX").has(sanitizedValue());
 		assertThatApplyingToKey(function, "YY").has(sanitizedValue());
 		assertThatApplyingToKey(function, "xy").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -182,7 +178,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToKey(function, "SPRING").has(sanitizedValue());
 		assertThatApplyingToKey(function, "BOOT").has(sanitizedValue());
 		assertThatApplyingToKey(function, "xspring").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -192,7 +187,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToKey(function, "spin").has(sanitizedValue());
 		assertThatApplyingToKey(function, "SPRING").has(unsanitizedValue());
 		assertThatApplyingToKey(function, "xspring").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -204,7 +198,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToKey(function, "BO").has(sanitizedValue());
 		assertThatApplyingToKey(function, "SPRING").has(unsanitizedValue());
 		assertThatApplyingToKey(function, "boot").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -213,7 +206,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToKey(function, "spring").has(sanitizedValue());
 		assertThatApplyingToKey(function, "spin").has(sanitizedValue());
 		assertThatApplyingToKey(function, "boot").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -223,7 +215,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToValue(function, "SPRING").has(sanitizedValue());
 		assertThatApplyingToValue(function, "boot").has(sanitizedValue());
 		assertThatApplyingToValue(function, "other").has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test
@@ -281,7 +272,6 @@ class SanitizingFunctionTests {
 		assertThatApplyingToValue(function, "spin").has(sanitizedValue());
 		assertThatApplyingToValue(function, "boot").has(unsanitizedValue());
 		assertThatApplyingToValue(function, 123).has(unsanitizedValue());
-		assertThatApplyingToKey(function, null).has(unsanitizedValue());
 	}
 
 	@Test