🐛 Fix NPE

kernel/sql/database.go

@@ -1316,6 +1316,9 @@ func queryRow(query string, args ...interface{}) *sql.Row {
 		logging.LogErrorf("statement is empty")
 		return nil
 	}
+	if nil == db {
+		return nil
+	}
 	return db.QueryRow(query, args...)
 }
 
@@ -1324,6 +1327,9 @@ func query(query string, args ...interface{}) (*sql.Rows, error) {
 	if "" == query {
 		return nil, errors.New("statement is empty")
 	}
+	if nil == db {
+		return nil, errors.New("database is nil")
+	}
 	return db.Query(query, args...)
 }