diff --git a/erpnext/patches/v13_0/add_bin_unique_constraint.py b/erpnext/patches/v13_0/add_bin_unique_constraint.py
index 29ae631..979fcf5 100644
--- a/erpnext/patches/v13_0/add_bin_unique_constraint.py
+++ b/erpnext/patches/v13_0/add_bin_unique_constraint.py
@@ -11,35 +11,47 @@
 
 
 def execute():
+	delete_broken_bins()
+	delete_and_patch_duplicate_bins()
 
-	duplicate_rows = frappe.db.sql("""
+def delete_broken_bins():
+	# delete useless bins
+	frappe.db.sql("delete from `tabBin` where item_code is null or warehouse is null")
+
+def delete_and_patch_duplicate_bins():
+
+	duplicate_bins = frappe.db.sql("""
 		SELECT
-		item_code, warehouse
+			item_code, warehouse, count(*) as bin_count
 		FROM
 			tabBin
 		GROUP BY
 			item_code, warehouse
 		HAVING
-			COUNT(*) > 1
+			bin_count > 1
 	""", as_dict=1)
 
-	for row in duplicate_rows:
-		bins = frappe.get_list("Bin",
-							   filters={"item_code": row.item_code,
-										"warehouse": row.warehouse},
-							   fields=["name"],
-							   order_by="creation",
-							   )
+	for duplicate_bin in duplicate_bins:
+		existing_bins = frappe.get_list("Bin",
+				filters={
+					"item_code": duplicate_bin.item_code,
+					"warehouse": duplicate_bin.warehouse
+					},
+				fields=["name"],
+				order_by="creation",)
 
-		for x in range(len(bins) - 1):
-			frappe.delete_doc("Bin", bins[x].name)
+		# keep last one
+		existing_bins.pop()
+
+		for broken_bin in existing_bins:
+			frappe.delete_doc("Bin", broken_bin.name)
 
 		qty_dict = {
-			"reserved_qty": get_reserved_qty(row.item_code, row.warehouse),
-			"indented_qty": get_indented_qty(row.item_code, row.warehouse),
-			"ordered_qty": get_ordered_qty(row.item_code, row.warehouse),
-			"planned_qty": get_planned_qty(row.item_code, row.warehouse),
-			"actual_qty": get_balance_qty_from_sle(row.item_code, row.warehouse)
+			"reserved_qty": get_reserved_qty(duplicate_bin.item_code, duplicate_bin.warehouse),
+			"indented_qty": get_indented_qty(duplicate_bin.item_code, duplicate_bin.warehouse),
+			"ordered_qty": get_ordered_qty(duplicate_bin.item_code, duplicate_bin.warehouse),
+			"planned_qty": get_planned_qty(duplicate_bin.item_code, duplicate_bin.warehouse),
+			"actual_qty": get_balance_qty_from_sle(duplicate_bin.item_code, duplicate_bin.warehouse)
 		}
 
-		update_bin_qty(row.item_code, row.warehouse, qty_dict)
+		update_bin_qty(duplicate_bin.item_code, duplicate_bin.warehouse, qty_dict)