Fix BaseCodecConfigurer clone bug

Prior to this commit, ExchangeStrategies custom codec's reader and
writer were not registered due to a bug in BaseCodecConfigurer.

This commit fixes this by correcting the implementation of the
DefaultCustomCodecs constructor used within BaseCodecConfigurer.

Closes gh-25149

spring-web/src/main/java/org/springframework/http/codec/support/BaseCodecConfigurer.java

@@ -142,10 +142,10 @@ abstract class BaseCodecConfigurer implements CodecConfigurer {
 		 * @since 5.1.12
 		 */
 		DefaultCustomCodecs(DefaultCustomCodecs other) {
-			other.typedReaders.putAll(this.typedReaders);
-			other.typedWriters.putAll(this.typedWriters);
-			other.objectReaders.putAll(this.objectReaders);
-			other.objectWriters.putAll(this.objectWriters);
+			this.typedReaders.putAll(other.typedReaders);
+			this.typedWriters.putAll(other.typedWriters);
+			this.objectReaders.putAll(other.objectReaders);
+			this.objectWriters.putAll(other.objectWriters);
 		}
 
 		@Override

spring-web/src/test/java/org/springframework/http/codec/support/CodecConfigurerTests.java

@@ -273,7 +273,7 @@ public class CodecConfigurerTests {
 	}
 
 	@Test
-	public void cloneCustomCodecs() {
+	public void cloneEmptyCustomCodecs() {
 		this.configurer.registerDefaults(false);
 		CodecConfigurer clone = this.configurer.clone();
 
@@ -288,6 +288,22 @@ public class CodecConfigurerTests {
 		assertEquals(2, clone.getWriters().size());
 	}
 
+	@Test
+	public void cloneCustomCodecs() {
+		CodecConfigurer from = new TestCodecConfigurer();
+		from.registerDefaults(false);
+		from.customCodecs().register(new Jackson2JsonEncoder());
+		from.customCodecs().register(new Jackson2JsonDecoder());
+		from.customCodecs().register(new ServerSentEventHttpMessageReader());
+		from.customCodecs().register(new ServerSentEventHttpMessageWriter());
+
+		CodecConfigurer clone = from.clone();
+		assertEquals(2, from.getReaders().size());
+		assertEquals(2, from.getWriters().size());
+		assertEquals(2, clone.getReaders().size());
+		assertEquals(2, clone.getWriters().size());
+	}
+
 	@Test
 	public void cloneDefaultCodecs() {
 		CodecConfigurer clone = this.configurer.clone();