Fix null customizer checks in HTTP client builders

AbstractClientHttpRequestFactoryBuilder.mergedCustomizers and its
reactive counterpart asserted on the customizers field rather than
the customizer parameter. The field is never null since the
constructor defaults it to an empty list, so the assertion always
passed and a null customizer was not rejected.

See gh-51509

Signed-off-by: kdomo <dongho5088@naver.com>

module/spring-boot-http-client/src/main/java/org/springframework/boot/http/client/AbstractClientHttpRequestFactoryBuilder.java

@@ -48,7 +48,7 @@ abstract class AbstractClientHttpRequestFactoryBuilder<T extends ClientHttpReque
 	}
 
 	protected final List<Consumer<T>> mergedCustomizers(Consumer<T> customizer) {
-		Assert.notNull(this.customizers, "'customizer' must not be null");
+		Assert.notNull(customizer, "'customizer' must not be null");
 		return merge(this.customizers, List.of(customizer));
 	}
 

module/spring-boot-http-client/src/main/java/org/springframework/boot/http/client/reactive/AbstractClientHttpConnectorBuilder.java

@@ -49,7 +49,7 @@ abstract class AbstractClientHttpConnectorBuilder<T extends ClientHttpConnector>
 	}
 
 	protected final List<Consumer<T>> mergedCustomizers(Consumer<T> customizer) {
-		Assert.notNull(this.customizers, "'customizer' must not be null");
+		Assert.notNull(customizer, "'customizer' must not be null");
 		return merge(this.customizers, List.of(customizer));
 	}
 

module/spring-boot-http-client/src/main/java/org/springframework/boot/http/client/reactive/ClientHttpConnectorBuilder.java

@@ -139,7 +139,7 @@ public interface ClientHttpConnectorBuilder<T extends ClientHttpConnector> {
 	 */
 	@SuppressWarnings("unchecked")
 	static <T extends ClientHttpConnector> ClientHttpConnectorBuilder<T> of(Class<T> clientHttpConnectorType) {
-		Assert.notNull(clientHttpConnectorType, "'requestFactoryType' must not be null");
+		Assert.notNull(clientHttpConnectorType, "'clientHttpConnectorType' must not be null");
 		Assert.isTrue(clientHttpConnectorType != ClientHttpConnector.class,
 				"'clientHttpConnectorType' must be an implementation of ClientHttpConnector");
 		if (clientHttpConnectorType == ReactorClientHttpConnector.class) {

module/spring-boot-http-client/src/main/java/org/springframework/boot/http/client/reactive/HttpComponentsClientHttpConnectorBuilder.java

@@ -66,7 +66,7 @@ public final class HttpComponentsClientHttpConnectorBuilder
 	 */
 	public HttpComponentsClientHttpConnectorBuilder withHttpClientCustomizer(
 			Consumer<HttpAsyncClientBuilder> httpClientCustomizer) {
-		Assert.notNull(httpClientCustomizer, "'customizer' must not be null");
+		Assert.notNull(httpClientCustomizer, "'httpClientCustomizer' must not be null");
 		return new HttpComponentsClientHttpConnectorBuilder(getCustomizers(),
 				this.httpClientBuilder.withCustomizer(httpClientCustomizer));
 	}

module/spring-boot-http-client/src/test/java/org/springframework/boot/http/client/SimpleClientHttpRequestFactoryBuilderTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.http.client;
 
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 
@@ -25,6 +26,7 @@ import org.springframework.http.client.SimpleClientHttpRequestFactory;
 import org.springframework.test.util.ReflectionTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 
 /**
@@ -81,6 +83,14 @@ class SimpleClientHttpRequestFactoryBuilderTests
 		super.redirectDontFollow(httpMethod);
 	}
 
+	@Test
+	@SuppressWarnings("NullAway") // Test null check
+	void withCustomizerWhenCustomizerIsNullThrowsException() {
+		assertThatIllegalArgumentException()
+				.isThrownBy(() -> ClientHttpRequestFactoryBuilder.simple().withCustomizer(null))
+				.withMessage("'customizer' must not be null");
+	}
+
 	@Override
 	protected HttpStatus getExpectedRedirect(HttpMethod httpMethod) {
 		return (httpMethod != HttpMethod.GET) ? HttpStatus.FOUND : HttpStatus.OK;

module/spring-boot-http-client/src/test/java/org/springframework/boot/http/client/reactive/HttpComponentsClientHttpConnectorBuilderTests.java

@@ -39,6 +39,7 @@ import org.springframework.http.client.reactive.HttpComponentsClientHttpConnecto
 import org.springframework.test.util.ReflectionTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 
 /**
  * Tests for {@link HttpComponentsClientHttpConnectorBuilder} and
@@ -80,6 +81,14 @@ class HttpComponentsClientHttpConnectorBuilderTests
 		defaultRequestConfigCustomizer1.assertCalled();
 	}
 
+	@Test
+	@SuppressWarnings("NullAway") // Test null check
+	void withHttpClientCustomizerWhenCustomizerIsNullThrowsException() {
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> ClientHttpConnectorBuilder.httpComponents().withHttpClientCustomizer(null))
+			.withMessage("'httpClientCustomizer' must not be null");
+	}
+
 	@Test
 	@WithPackageResources("test.jks")
 	void withTlsSocketStrategyFactory() {

module/spring-boot-http-client/src/test/java/org/springframework/boot/http/client/reactive/JdkClientHttpConnectorBuilderTests.java

@@ -28,6 +28,7 @@ import org.springframework.http.client.reactive.JdkClientHttpConnector;
 import org.springframework.test.util.ReflectionTestUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 
 /**
  * Tests for {@link JdkClientHttpConnectorBuilder} and {@link JdkHttpClientBuilder}.
@@ -52,6 +53,13 @@ class JdkClientHttpConnectorBuilderTests extends AbstractClientHttpConnectorBuil
 		httpClientCustomizer2.assertCalled();
 	}
 
+	@Test
+	@SuppressWarnings("NullAway") // Test null check
+	void withCustomizerWhenCustomizerIsNullThrowsException() {
+		assertThatIllegalArgumentException().isThrownBy(() -> ClientHttpConnectorBuilder.jdk().withCustomizer(null))
+			.withMessage("'customizer' must not be null");
+	}
+
 	@Test
 	void withExecutor() {
 		Executor executor = new SimpleAsyncTaskExecutor();