[fix](catalog)fix db name may be null in NotificationEvent (#38421)

cause by: #29059

Author: zddr

fe/fe-core/src/main/java/org/apache/doris/datasource/hive/event/MetastoreEvent.java

@@ -21,6 +21,7 @@
 import org.apache.doris.datasource.hive.HMSCachedClient;
 
 import com.google.common.collect.ImmutableList;
+import org.apache.commons.lang3.StringUtils;
 import org.apache.hadoop.hive.metastore.api.NotificationEvent;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -79,7 +80,9 @@ protected MetastoreEvent(long eventId, String catalogName, String dbName,
 
     protected MetastoreEvent(NotificationEvent event, String catalogName) {
         this.event = event;
-        this.dbName = event.getDbName().toLowerCase(Locale.ROOT);
+        // Some events that we don't care about, dbName may be empty
+        String eventDbName = event.getDbName();
+        this.dbName = StringUtils.isEmpty(eventDbName) ? eventDbName : eventDbName.toLowerCase(Locale.ROOT);
         this.tblName = event.getTableName();
         this.eventId = event.getEventId();
         this.eventTime = event.getEventTime() * 1000L;