From b5c89c91a9aa3a8f6e2e58869da126c6c8e045bf Mon Sep 17 00:00:00 2001
From: Brian Clozel <brian.clozel@broadcom.com>
Date: Fri, 21 Feb 2025 14:23:12 +0100
Subject: [PATCH] Handle null values in MockHttpServletResponse#setHeader

Prior to this commit, `MockHttpServletResponse#setHeader` would not
remove the header entry when given a `null` value, as documented in the
Servlet API.
This commit ensures that this behavior is enforced.

Fixes gh-34466
---
 .../mock/web/MockHttpServletResponse.java            |  7 ++++++-
 .../mock/web/MockHttpServletResponseTests.java       | 12 ++++++++++++
 .../testfixture/servlet/MockHttpServletResponse.java |  7 ++++++-
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/spring-test/src/main/java/org/springframework/mock/web/MockHttpServletResponse.java b/spring-test/src/main/java/org/springframework/mock/web/MockHttpServletResponse.java
index 19e8753e4fe..03b54d6a01e 100644
--- a/spring-test/src/main/java/org/springframework/mock/web/MockHttpServletResponse.java
+++ b/spring-test/src/main/java/org/springframework/mock/web/MockHttpServletResponse.java
@@ -671,7 +671,12 @@ public class MockHttpServletResponse implements HttpServletResponse {
 
 	@Override
 	public void setHeader(String name, @Nullable String value) {
-		setHeaderValue(name, value);
+		if (value == null) {
+			this.headers.remove(name);
+		}
+		else {
+			setHeaderValue(name, value);
+		}
 	}
 
 	@Override
diff --git a/spring-test/src/test/java/org/springframework/mock/web/MockHttpServletResponseTests.java b/spring-test/src/test/java/org/springframework/mock/web/MockHttpServletResponseTests.java
index 6d5c92007d1..e3177c8f0b8 100644
--- a/spring-test/src/test/java/org/springframework/mock/web/MockHttpServletResponseTests.java
+++ b/spring-test/src/test/java/org/springframework/mock/web/MockHttpServletResponseTests.java
@@ -87,6 +87,18 @@ class MockHttpServletResponseTests {
 		assertThat(response.containsHeader(headerName)).isFalse();
 	}
 
+	@ParameterizedTest
+	@ValueSource(strings = {
+			CONTENT_TYPE,
+			CONTENT_LANGUAGE,
+			"X-Test-Header"
+	})
+	void removeHeaderIfNullValue(String headerName) {
+		response.addHeader(headerName, "test");
+		response.setHeader(headerName, null);
+		assertThat(response.containsHeader(headerName)).isFalse();
+	}
+
 	@Test  // gh-26493
 	void setLocaleWithNullValue() {
 		assertThat(response.getLocale()).isEqualTo(Locale.getDefault());
diff --git a/spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockHttpServletResponse.java b/spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockHttpServletResponse.java
index 9ced4d59b1a..9e29ad3a603 100644
--- a/spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockHttpServletResponse.java
+++ b/spring-web/src/testFixtures/java/org/springframework/web/testfixture/servlet/MockHttpServletResponse.java
@@ -671,7 +671,12 @@ public class MockHttpServletResponse implements HttpServletResponse {
 
 	@Override
 	public void setHeader(String name, @Nullable String value) {
-		setHeaderValue(name, value);
+		if (value == null) {
+			this.headers.remove(name);
+		}
+		else {
+			setHeaderValue(name, value);
+		}
 	}
 
 	@Override