Describe the bug
Even if the connection string property is set as empty, the application still tries to auth via connection string.

The application is a simple spring cloud stream + kafka, refering to the sample project https://github.com/Azure-Samples/azure-spring-boot-samples/tree/main/eventhubs/spring-cloud-azure-starter/spring-cloud-azure-sample-eventhubs-kafka.

In the application.yaml, when we specify the auth as follows, we want to use managed identity auth, instead of connection string (we leave it empty), but the application still try to use connection string for auth, causing it cannot startup.

spring:
  cloud:
        azure:
          eventhubs:
            credential:
              managed-identity-enabled: true
              client-id:  XXX
          connection-string:  # empty string

Exception or Stack Trace

In the following file, when the property is set as empty, it should not enter the method. but now it will execute this method even if empty.

public class AzureEventHubsKafkaAutoConfiguration {

    private static final Logger LOGGER = LoggerFactory.getLogger(AzureEventHubsKafkaAutoConfiguration.class);

    @Bean
    @ConditionalOnProperty("spring.cloud.azure.eventhubs.connection-string")
    @ConditionalOnMissingBean(value = AzureServiceType.EventHubs.class, parameterizedContainer = ServiceConnectionStringProvider.class)
    StaticConnectionStringProvider<AzureServiceType.EventHubs> eventHubsKafkaConnectionString(Environment environment) {
        String connectionString = environment.getProperty("spring.cloud.azure.eventhubs.connection-string");

        try {
            new EventHubsConnectionString(connectionString);
        } catch (Exception e) {
            LOGGER.error("A valid Event Hubs connection string must be provided");
            throw e;
        }

        return new StaticConnectionStringProvider<>(AzureServiceType.EVENT_HUBS, connectionString);
    }

To Reproduce
Steps to reproduce the behavior:

1. Clone the sample project.
2. As described above, specify the application properties and then run.

Code Snippet
Add the code snippet that causes the issue.

Expected behavior

When setting connection string as empty, it should auto-use MI configuration for auth.

Screenshots
If applicable, add screenshots to help explain your problem.

Setup (please complete the following information):

• OS: [e.g. iOS] Windows 11
• IDE: [e.g. IntelliJ]: IDEA
• Library/Libraries: spring-boot-starter-web 3.3.5, spring-cloud-starter-stream-kafka 4.1.3, spring-cloud-azure-starter 5.18.0
• Java version: [e.g. 8] 17
• App Server/Environment: Tomcat
• Frameworks: Spring Boot

If you suspect a dependency version mismatch (e.g. you see NoClassDefFoundError, NoSuchMethodError or similar), please check out Troubleshoot dependency version conflict article first. If it doesn't provide solution for the problem, please provide:

• verbose dependency tree (mvn dependency:tree -Dverbose)
• exception message, full stack trace, and any available logs

Additional context
Add any other context about the problem here.

Information Checklist
Kindly make sure that you have added all the following information above and checkoff the required fields otherwise we will treat the issuer as an incomplete report

• Bug Description Added
• Repro Steps Added
• Setup information Added