fix: avoid calling .replace() on None (LAN-845)

landa/water_body_management/change_log.py

@@ -155,7 +155,7 @@ def _build_modified_change_log(self, entry, changed_data, event):
 
 			# Newlines have been converted to <br> in the Version log
 			# Convert them back to newlines for consistency with the other endpoints
-			if frappe.get_meta(entry.doctype).get_field(key).fieldtype in ("Text", "Small Text"):
+			if data and frappe.get_meta(entry.doctype).get_field(key).fieldtype in ("Text", "Small Text"):
 				data = data.replace("<br>", "\n")
 
 			if row[0] == "location":