May this help:
You should find the patches.txt in the apps/erpnext/erpnext directory or
in apps/frappe/frappe.
Open it with an editor /nano in ubuntu/.
Then find the misslead
frappe.patch
frappe.patches.v8_1.enable_allow_error_traceback_in_system_settings
and comment out /# /
Then run bench migrate.
It should run smoothly then go to you site and add the necessary currency precision.
Then clear out the commented row.
Run bench update --upgrade again.
OR
as advised before if you are in the system,
go to the specific Doctype and reset it.
Hope this helps.