Make BytesEncoder back off without an Encoding bean

Closes gh-46153

spring-boot-project/spring-boot-tracing/src/main/java/org/springframework/boot/tracing/autoconfigure/zipkin/ZipkinTracingAutoConfiguration.java

@@ -83,6 +83,7 @@ public class ZipkinTracingAutoConfiguration {
 	static class OpenTelemetryConfiguration {
 
 		@Bean
+		@ConditionalOnBean(Encoding.class)
 		@ConditionalOnMissingBean(value = Span.class, parameterizedContainer = BytesEncoder.class)
 		BytesEncoder<Span> spanBytesEncoder(Encoding encoding) {
 			return SpanBytesEncoder.forEncoding(encoding);

spring-boot-project/spring-boot-tracing/src/test/java/org/springframework/boot/tracing/autoconfigure/zipkin/ZipkinConfigurationsOpenTelemetryConfigurationTests.java

@@ -42,6 +42,15 @@ class ZipkinConfigurationsOpenTelemetryConfigurationTests {
 	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
 		.withConfiguration(AutoConfigurations.of(DefaultEncodingConfiguration.class, OpenTelemetryConfiguration.class));
 
+	@Test
+	void backsOffWithoutEncoding() {
+		new ApplicationContextRunner().withUserConfiguration(OpenTelemetryConfiguration.class).run((context) -> {
+			assertThat(context).hasNotFailed();
+			assertThat(context).doesNotHaveBean(ZipkinSpanExporter.class);
+			assertThat(context).doesNotHaveBean(BytesEncoder.class);
+		});
+	}
+
 	@Test
 	void shouldSupplyBeans() {
 		this.contextRunner.withUserConfiguration(SenderConfiguration.class, CustomEncoderConfiguration.class)