采购计划生产时，如果之前有采购建议未更新

AutoTurnOver.Models/dc_auto_purchase_advise.cs

@@ -52,6 +52,7 @@ namespace AutoTurnOver.Models
         /// sku
         /// </summary>
         public string bailun_sku { get; set; }
+        public DateTime? create_time { get; set; }
         public string bailun_sku_warehouse_code { get; set; }
 
         /// <summary>
@@ -362,7 +363,14 @@ namespace AutoTurnOver.Models
         /// 工作日
         /// </summary>
         public int working_days { get {
-                return WorkingDays(create_time,DateTime.Now);
+                if (create_time != null)
+                {
+                    return WorkingDays(create_time.Value, DateTime.Now);
+                }
+                else
+                {
+                    return 0;
+                }
             } }
 
         public bool has_overdue { get
@@ -431,9 +439,8 @@ namespace AutoTurnOver.Models
 
         public string sku_name { get; set; }
 
-        public DateTime create_time { get; set; }
 
-        public string create_time_str { get { return create_time.ToString("yyyy-MM-dd HH:mm"); } }
+        public string create_time_str { get { if (create_time == null) return "";  return create_time.Value.ToString("yyyy-MM-dd HH:mm"); } }
 
         /// <summary>
         /// 日均加权销量