From 23625ee6982557435557697d05793b1d655ab431 Mon Sep 17 00:00:00 2001
From: Brian Clozel <brian.clozel@broadcom.com>
Date: Thu, 11 Dec 2025 09:40:42 +0100
Subject: [PATCH] Do not send null HTTP header value in JdkClientHttpRequest

Prior to this commit, the `JdkClientHttpRequest` would add all values
from `HttpHeaders` to the native request builder. This could cause
`NullPointerException` being thrown at runtime because the `HttpClient`
does not support that.

This commit replicates a fix that was applied to the
`SimpleClientHttpRequest`, turning null values into empty "".

Fixes gh-35996
---
 .../http/client/JdkClientHttpRequest.java     |  2 +-
 .../http/client/OkHttp3ClientHttpRequest.java |  2 +-
 .../client/RestClientIntegrationTests.java    | 23 +++++++++++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequest.java b/spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequest.java
index 0d14667f83a..73157f5ab9a 100644
--- a/spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequest.java
+++ b/spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequest.java
@@ -155,7 +155,7 @@ class JdkClientHttpRequest extends AbstractStreamingClientHttpRequest {
 		headers.forEach((headerName, headerValues) -> {
 			if (!DISALLOWED_HEADERS.contains(headerName.toLowerCase(Locale.ROOT))) {
 				for (String headerValue : headerValues) {
-					builder.header(headerName, headerValue);
+					builder.header(headerName, (headerValue != null) ? headerValue : "");
 				}
 			}
 		});
diff --git a/spring-web/src/main/java/org/springframework/http/client/OkHttp3ClientHttpRequest.java b/spring-web/src/main/java/org/springframework/http/client/OkHttp3ClientHttpRequest.java
index 9ead1f58c30..25de1587fb2 100644
--- a/spring-web/src/main/java/org/springframework/http/client/OkHttp3ClientHttpRequest.java
+++ b/spring-web/src/main/java/org/springframework/http/client/OkHttp3ClientHttpRequest.java
@@ -90,7 +90,7 @@ class OkHttp3ClientHttpRequest extends AbstractStreamingClientHttpRequest {
 		builder.method(this.method.name(), requestBody);
 		headers.forEach((headerName, headerValues) -> {
 			for (String headerValue : headerValues) {
-				builder.addHeader(headerName, headerValue);
+				builder.addHeader(headerName, (headerValue != null) ? headerValue : "");
 			}
 		});
 		Request request = builder.build();
diff --git a/spring-web/src/test/java/org/springframework/web/client/RestClientIntegrationTests.java b/spring-web/src/test/java/org/springframework/web/client/RestClientIntegrationTests.java
index fe1c9e07fb0..9fbd9ad7c4d 100644
--- a/spring-web/src/test/java/org/springframework/web/client/RestClientIntegrationTests.java
+++ b/spring-web/src/test/java/org/springframework/web/client/RestClientIntegrationTests.java
@@ -961,6 +961,29 @@ class RestClientIntegrationTests {
 		expectRequest(request -> assertThat(request.getHeader("foo")).isEqualTo("bar"));
 	}
 
+
+	@ParameterizedRestClientTest
+	void sendNullHeaderValue(ClientHttpRequestFactory requestFactory) throws IOException {
+		startServer(requestFactory);
+
+		prepareResponse(builder -> builder
+				.setHeader("Content-Type", "text/plain").setBody("Hello Spring!"));
+
+		String result = this.restClient.get()
+				.uri("/greeting")
+				.httpRequest(request -> request.getHeaders().add("X-Test-Header", null))
+				.retrieve()
+				.body(String.class);
+
+		assertThat(result).isEqualTo("Hello Spring!");
+
+		expectRequestCount(1);
+		expectRequest(request -> {
+			assertThat(request.getHeaders().get("X-Test-Header")).isNullOrEmpty();
+			assertThat(request.getPath()).isEqualTo("/greeting");
+		});
+	}
+
 	@ParameterizedRestClientTest
 	void defaultRequest(ClientHttpRequestFactory requestFactory) {
 		startServer(requestFactory);