fix posdetail view when no pos json yet

src/economy/models.py

@@ -853,6 +853,7 @@ class PosReport(CampRelatedModel, UUIDModel):
         """Calculate the total HAX sales and number of transactions."""
         transactions = 0
         total = 0
+        if self.pos_json:
             for tx in self.pos_json:
                 transactions += 1
                 total += tx["amount"]