Improve null-safety of module/spring-boot-mongodb

See gh-47263

module/spring-boot-mongodb/src/main/java/org/springframework/boot/mongodb/autoconfigure/MongoClientFactory.java

@@ -20,6 +20,7 @@ import java.util.List;
 
 import com.mongodb.client.MongoClient;
 import com.mongodb.client.MongoClients;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A factory for a blocking {@link MongoClient}.
@@ -41,7 +42,7 @@ public class MongoClientFactory extends MongoClientFactorySupport<MongoClient> {
 	 * Construct a factory for creating a blocking {@link MongoClient}.
 	 * @param builderCustomizers a list of configuration settings customizers
 	 */
-	public MongoClientFactory(List<MongoClientSettingsBuilderCustomizer> builderCustomizers) {
+	public MongoClientFactory(@Nullable List<MongoClientSettingsBuilderCustomizer> builderCustomizers) {
 		super(builderCustomizers, MongoClients::create);
 	}
 

module/spring-boot-mongodb/src/main/java/org/springframework/boot/mongodb/autoconfigure/ReactiveMongoClientFactory.java

@@ -20,6 +20,7 @@ import java.util.List;
 
 import com.mongodb.reactivestreams.client.MongoClient;
 import com.mongodb.reactivestreams.client.MongoClients;
+import org.jspecify.annotations.Nullable;
 
 /**
  * A factory for a reactive {@link MongoClient}.
@@ -35,7 +36,7 @@ public class ReactiveMongoClientFactory extends MongoClientFactorySupport<MongoC
 	 * Construct a factory for creating a {@link MongoClient}.
 	 * @param builderCustomizers a list of configuration settings customizers
 	 */
-	public ReactiveMongoClientFactory(List<MongoClientSettingsBuilderCustomizer> builderCustomizers) {
+	public ReactiveMongoClientFactory(@Nullable List<MongoClientSettingsBuilderCustomizer> builderCustomizers) {
 		super(builderCustomizers, MongoClients::create);
 	}