fix: misleading "Set Default X" fields after saving (#28798)

* fix: misleading "Set Default X" fields after saving

* refactor: remove unncessary code and minor formatting

* fix: extend to more doctypes and correct fieldnames

Co-authored-by: Ankush Menat <ankush@frappe.io>

erpnext/controllers/tests/test_transaction_base.py

@@ -0,0 +1,22 @@
+import unittest
+
+import frappe
+
+
+class TestUtils(unittest.TestCase):
+    def test_reset_default_field_value(self):
+        doc = frappe.get_doc({
+            "doctype": "Purchase Receipt",
+            "set_warehouse": "Warehouse 1",
+        })
+
+        # Same values
+        doc.items = [{"warehouse": "Warehouse 1"}, {"warehouse": "Warehouse 1"}, {"warehouse": "Warehouse 1"}]
+        doc.reset_default_field_value("set_warehouse", "items", "warehouse")
+        self.assertEqual(doc.set_warehouse, "Warehouse 1")
+
+        # Mixed values
+        doc.items = [{"warehouse": "Warehouse 1"}, {"warehouse": "Warehouse 2"}, {"warehouse": "Warehouse 1"}]
+        doc.reset_default_field_value("set_warehouse", "items", "warehouse")
+        self.assertEqual(doc.set_warehouse, None)
+