Support blank MongoDB 'replica-set-name' properties

Update `null` checks to `StringUtils.hasText` to allow the
`replica-set-name' property to be overridden with an empty string.

Fixes gh-42055

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mongo/MongoPropertiesClientSettingsBuilderCustomizer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,6 +26,7 @@
 
 import org.springframework.core.Ordered;
 import org.springframework.util.CollectionUtils;
+import org.springframework.util.StringUtils;
 
 /**
  * A {@link MongoClientSettingsBuilderCustomizer} that applies properties from a
@@ -90,7 +91,7 @@ private void applyCredentials(MongoClientSettings.Builder builder) {
 	}
 
 	private void applyReplicaSet(MongoClientSettings.Builder builder) {
-		if (this.properties.getReplicaSetName() != null) {
+		if (StringUtils.hasText(this.properties.getReplicaSetName())) {
 			builder.applyToClusterSettings(
 					(cluster) -> cluster.requiredReplicaSetName(this.properties.getReplicaSetName()));
 		}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mongo/PropertiesMongoConnectionDetails.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,6 +23,8 @@
 
 import com.mongodb.ConnectionString;
 
+import org.springframework.util.StringUtils;
+
 /**
  * Adapts {@link MongoProperties} to {@link MongoConnectionDetails}.
  *
@@ -90,7 +92,7 @@ public GridFs getGridFs() {
 
 	private List<String> getOptions() {
 		List<String> options = new ArrayList<>();
-		if (this.properties.getReplicaSetName() != null) {
+		if (StringUtils.hasText(this.properties.getReplicaSetName())) {
 			options.add("replicaSet=" + this.properties.getReplicaSetName());
 		}
 		if (this.properties.getUsername() != null && this.properties.getAuthenticationDatabase() != null) {

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/mongo/MongoPropertiesClientSettingsBuilderCustomizerTests.java

@@ -22,6 +22,7 @@
 import com.mongodb.MongoClientSettings;
 import com.mongodb.MongoCredential;
 import com.mongodb.ServerAddress;
+import com.mongodb.connection.ClusterType;
 import org.bson.UuidRepresentation;
 import org.junit.jupiter.api.Test;
 
@@ -81,6 +82,23 @@ void replicaSetCanBeCustomized() {
 		this.properties.setReplicaSetName("test");
 		MongoClientSettings settings = customizeSettings();
 		assertThat(settings.getClusterSettings().getRequiredReplicaSetName()).isEqualTo("test");
+		assertThat(settings.getClusterSettings().getRequiredClusterType()).isEqualTo(ClusterType.REPLICA_SET);
+	}
+
+	@Test
+	void replicaSetCanBeNull() {
+		this.properties.setReplicaSetName(null);
+		MongoClientSettings settings = customizeSettings();
+		assertThat(settings.getClusterSettings().getRequiredReplicaSetName()).isNull();
+		assertThat(settings.getClusterSettings().getRequiredClusterType()).isEqualTo(ClusterType.UNKNOWN);
+	}
+
+	@Test
+	void replicaSetCanBeEmptyString() {
+		this.properties.setReplicaSetName("");
+		MongoClientSettings settings = customizeSettings();
+		assertThat(settings.getClusterSettings().getRequiredReplicaSetName()).isNull();
+		assertThat(settings.getClusterSettings().getRequiredClusterType()).isEqualTo(ClusterType.UNKNOWN);
 	}
 
 	@Test

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/mongo/PropertiesMongoConnectionDetailsTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -104,6 +104,20 @@ void replicaSetCanBeConfiguredWithDatabase() {
 		assertThat(connectionString.getRequiredReplicaSetName()).isEqualTo("test");
 	}
 
+	@Test
+	void replicaSetCanBeNull() {
+		this.properties.setReplicaSetName(null);
+		ConnectionString connectionString = getConnectionString();
+		assertThat(connectionString.getRequiredReplicaSetName()).isNull();
+	}
+
+	@Test
+	void replicaSetCanBeBlank() {
+		this.properties.setReplicaSetName("");
+		ConnectionString connectionString = getConnectionString();
+		assertThat(connectionString.getRequiredReplicaSetName()).isNull();
+	}
+
 	@Test
 	void whenAdditionalHostsAreConfiguredThenTheyAreIncludedInHostsOfConnectionString() {
 		this.properties.setHost("mongo1.example.com");