diff --git a/spring-test/src/main/java/org/springframework/mock/web/MockMultipartFile.java b/spring-test/src/main/java/org/springframework/mock/web/MockMultipartFile.java
index 359d945a1d3e..781ab7a6e48f 100644
--- a/spring-test/src/main/java/org/springframework/mock/web/MockMultipartFile.java
+++ b/spring-test/src/main/java/org/springframework/mock/web/MockMultipartFile.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -21,6 +21,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 
+import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.FileCopyUtils;
@@ -42,10 +43,10 @@ public class MockMultipartFile implements MultipartFile {
 
 	private final String name;
 
-	private String originalFilename;
+	private final String originalFilename;
 
 	@Nullable
-	private String contentType;
+	private final String contentType;
 
 	private final byte[] content;
 
@@ -79,7 +80,7 @@ public MockMultipartFile(String name, InputStream contentStream) throws IOExcept
 	public MockMultipartFile(
 			String name, @Nullable String originalFilename, @Nullable String contentType, @Nullable byte[] content) {
 
-		Assert.hasLength(name, "Name must not be null");
+		Assert.hasLength(name, "Name must not be empty");
 		this.name = name;
 		this.originalFilename = (originalFilename != null ? originalFilename : "");
 		this.contentType = contentType;
@@ -108,6 +109,7 @@ public String getName() {
 	}
 
 	@Override
+	@NonNull
 	public String getOriginalFilename() {
 		return this.originalFilename;
 	}
diff --git a/spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockMultipartFile.java b/spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockMultipartFile.java
index 9250fb076c11..849731ac5a68 100644
--- a/spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockMultipartFile.java
+++ b/spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockMultipartFile.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -21,6 +21,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 
+import org.springframework.lang.NonNull;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.FileCopyUtils;
@@ -42,10 +43,10 @@ public class MockMultipartFile implements MultipartFile {
 
 	private final String name;
 
-	private String originalFilename;
+	private final String originalFilename;
 
 	@Nullable
-	private String contentType;
+	private final String contentType;
 
 	private final byte[] content;
 
@@ -79,7 +80,7 @@ public MockMultipartFile(String name, InputStream contentStream) throws IOExcept
 	public MockMultipartFile(
 			String name, @Nullable String originalFilename, @Nullable String contentType, @Nullable byte[] content) {
 
-		Assert.hasLength(name, "Name must not be null");
+		Assert.hasLength(name, "Name must not be empty");
 		this.name = name;
 		this.originalFilename = (originalFilename != null ? originalFilename : "");
 		this.contentType = contentType;
@@ -108,6 +109,7 @@ public String getName() {
 	}
 
 	@Override
+	@NonNull
 	public String getOriginalFilename() {
 		return this.originalFilename;
 	}