修复bug

app/service/material_list.js

@@ -312,8 +312,8 @@ module.exports = app => {
                     xmj_id: ml.xmj_id,
                     mx_id: ml.mx_id,
                     gather_qty: ml.gather_qty,
-                    quantity: ml.quantity,
-                    expr: ml.expr,
+                    quantity: ml.quantity ? ml.quantity : 0,
+                    expr: ml.expr ? ml.expr : '',
                     is_join: is_join ? 0 : 1,
                     in_time: new Date(),
                 };