diff --git a/src/sql/engine/expr/ob_expr_sys_context.cpp b/src/sql/engine/expr/ob_expr_sys_context.cpp
index 902cf74af5..e86c79822f 100644
--- a/src/sql/engine/expr/ob_expr_sys_context.cpp
+++ b/src/sql/engine/expr/ob_expr_sys_context.cpp
@@ -762,7 +762,11 @@ int ObExprSysContext::eval_application_context(const ObExpr &expr, ObDatum &res,
   }
   if (OB_SUCC(ret)) {
     if (exist) {
-      OX(res.set_string(out_value));
+      if (out_value.empty()) {
+        res.set_null();
+      } else {
+        res.set_string(out_value);
+      }
     } else {
       res.set_null();
     }