diff --git a/be/src/olap/column_reader.cpp b/be/src/olap/column_reader.cpp
index 38e9cd35c2..13f7c6aefb 100644
--- a/be/src/olap/column_reader.cpp
+++ b/be/src/olap/column_reader.cpp
@@ -641,7 +641,6 @@ ColumnReader* ColumnReader::create(uint32_t column_id,
                         field_info.default_value, field_info.type, field_info.length);
             }
         } else if (field_info.is_allow_null) {
-            LOG(WARNING) << "create NullValueReader: " << field_info.name;
             return new(std::nothrow) NullValueReader(column_id, column_unique_id);
         } else {
             OLAP_LOG_WARNING("not null field has no default value");
diff --git a/be/src/olap/schema_change.cpp b/be/src/olap/schema_change.cpp
index a5c2a2c120..2e9c615104 100644
--- a/be/src/olap/schema_change.cpp
+++ b/be/src/olap/schema_change.cpp
@@ -2358,7 +2358,7 @@ OLAPStatus SchemaChangeHandler::_init_column_mapping(ColumnMapping* column_mappi
         return OLAP_ERR_MALLOC_ERROR;
     }
 
-    if (true == column_schema.is_allow_null && value.length() == 0) {
+    if (column_schema.is_allow_null && !column_schema.has_default_value) {
         column_mapping->default_value->set_null();
     } else {
         column_mapping->default_value->from_string(value);