Minor: Data Import test case

frappe/tests/test_data_import.py

@@ -75,7 +75,7 @@ class TestDataImport(unittest.TestCase):
 	def test_import_with_children(self):
 		exporter.get_template("Event", all_doctypes="Yes", with_data="No")
 		content = read_csv_content(frappe.response.result)
-		content.append([""] * len(content[-2]))
+		content.append([None] * len(content[-2]))
 		content[-1][2] = "__Test Event"
 		content[-1][3] = "Private"
 		content[-1][4] = "2014-01-01 10:00:00.000000"