Fixing the NullPointerException in RoutingDataSourceHealthContributor

The RoutingDataSourceHealthContributor constructor throws a NullPointerException (NPE) if the provided map has a null key. With this commit the NPE issue has been fixed by filtering the entries that are not-null. 

This closes spring-projects#27694

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/jdbc/DataSourceHealthContributorAutoConfiguration.java

@@ -127,6 +127,7 @@ static class RoutingDataSourceHealthContributor implements CompositeHealthContri
 		RoutingDataSourceHealthContributor(AbstractRoutingDataSource routingDataSource,
 				Function<DataSource, HealthContributor> contributorFunction) {
 			Map<String, DataSource> routedDataSources = routingDataSource.getResolvedDataSources().entrySet().stream()
+					.filter((e) -> e.getKey() != null)
 					.collect(Collectors.toMap((e) -> e.getKey().toString(), Map.Entry::getValue));
 			this.delegate = CompositeHealthContributor.fromMap(routedDataSources, contributorFunction);
 		}