diff --git a/api/src/main/java/com/databasir/job/ProjectSyncTaskScheduler.java b/api/src/main/java/com/databasir/job/ProjectSyncTaskScheduler.java
index 5586292..b38e6e4 100644
--- a/api/src/main/java/com/databasir/job/ProjectSyncTaskScheduler.java
+++ b/api/src/main/java/com/databasir/job/ProjectSyncTaskScheduler.java
@@ -54,7 +54,8 @@ public class ProjectSyncTaskScheduler {
             updateSyncTaskStatus(taskId, ProjectSyncTaskStatus.FINISHED, "ok");
             saveOperationLog(projectId, userId, null);
         } catch (Exception e) {
-            updateSyncTaskStatus(taskId, ProjectSyncTaskStatus.FAILED, e.getMessage());
+            String result = Objects.requireNonNullElse(e.getMessage(), "unknown");
+            updateSyncTaskStatus(taskId, ProjectSyncTaskStatus.FAILED, result);
             saveOperationLog(projectId, userId, e);
             throw e;
         }
diff --git a/core/src/main/java/com/databasir/core/domain/document/service/DocumentService.java b/core/src/main/java/com/databasir/core/domain/document/service/DocumentService.java
index beb6961..a1ffe4c 100644
--- a/core/src/main/java/com/databasir/core/domain/document/service/DocumentService.java
+++ b/core/src/main/java/com/databasir/core/domain/document/service/DocumentService.java
@@ -143,13 +143,16 @@ public class DocumentService {
         databasirConfig.setIgnoreTableNameRegex(jsonConverter.fromJson(rule.getIgnoreTableNameRegexArray()));
         databasirConfig.setIgnoreTableColumnNameRegex(jsonConverter.fromJson(rule.getIgnoreColumnNameRegexArray()));
         try {
+            if (jdbcConnection == null) {
+                throw DomainErrors.CONNECT_DATABASE_FAILED.exception();
+            }
             DatabaseMeta databaseMeta = Databasir.of(databasirConfig)
                     .get(jdbcConnection, dataSource.getDatabaseName(), dataSource.getSchemaName())
                     .orElseThrow(DomainErrors.DATABASE_META_NOT_FOUND::exception);
             return databaseMeta;
         } finally {
             try {
-                if (!jdbcConnection.isClosed()) {
+                if (jdbcConnection != null && !jdbcConnection.isClosed()) {
                     jdbcConnection.close();
                 }
             } catch (SQLException e) {