We are using Odoo 15 enterprise edition. We have customized unbuild order. While duplicate unbuild order I am getting the following error.

RPC_ERROR
Odoo Server Error
Traceback (most recent call last):
File "/opt/odoo/odoo15/odoo/odoo/addons/base/models/ir_http\.py",\ line\ 237,\ in\ _dispatch
\ \ \ \ result\ =\ request\.dispatch\(\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/http\.py",\ line\ 687,\ in\ dispatch
\ \ \ \ result\ =\ self\._call_function\(\*\*self\.params\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/http\.py",\ line\ 359,\ in\ _call_function
\ \ \ \ return\ checked_call\(self\.db,\ \*args,\ \*\*kwargs\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/service/model\.py",\ line\ 94,\ in\ wrapper
\ \ \ \ return\ f\(dbname,\ \*args,\ \*\*kwargs\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/http\.py",\ line\ 348,\ in\ checked_call
\ \ \ \ result\ =\ self\.endpoint\(\*a,\ \*\*kw\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/http\.py",\ line\ 916,\ in\ __call__
\ \ \ \ return\ self\.method\(\*args,\ \*\*kw\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/http\.py",\ line\ 535,\ in\ response_wrap
\ \ \ \ response\ =\ f\(\*args,\ \*\*kw\)
\ \ File\ "/opt/odoo/odoo15/odoo/addons/web/controllers/main\.py",\ line\ 1343,\ in\ call_kw
\ \ \ \ return\ self\._call_kw\(model,\ method,\ args,\ kwargs\)
\ \ File\ "/opt/odoo/odoo15/odoo/addons/web/controllers/main\.py",\ line\ 1335,\ in\ _call_kw
\ \ \ \ return\ call_kw\(request\.env\[model\],\ method,\ args,\ kwargs\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/api\.py",\ line\ 464,\ in\ call_kw
\ \ \ \ result\ =\ _call_kw_multi\(method,\ model,\ args,\ kwargs\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/api\.py",\ line\ 451,\ in\ _call_kw_multi
\ \ \ \ result\ =\ method\(recs,\ \*args,\ \*\*kwargs\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/models\.py",\ line\ 4864,\ in\ copy
\ \ \ \ vals\ =\ self\.with_context\(active_test=False\)\.copy_data\(default\)\[0\]
\ \ File\ "/opt/odoo/odoo15/odoo/addons/mail/models/mail_thread\.py",\ line\ 346,\ in\ copy_data
\ \ \ \ return\ super\(MailThread,\ self\.with_context\(mail_notrack=True\)\)\.copy_data\(default=default\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/models\.py",\ line\ 4768,\ in\ copy_data
\ \ \ \ lines\ =\ \[rec\.copy_data\(\)\[0\]\ for\ rec\ in\ self\[name\]\.sorted\(key='id'\)\]
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/models\.py",\ line\ 4768,\ in\
\ \ \ \ lines\ =\ \[rec\.copy_data\(\)\[0\]\ for\ rec\ in\ self\[name\]\.sorted\(key='id'\)\]
Exception

The\ above\ exception\ was\ the\ direct\ cause\ of\ the\ following\ exception:

Traceback\ \(most\ recent\ call\ last\):
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/http\.py",\ line\ 643,\ in\ _handle_exception
\ \ \ \ return\ super\(JsonRequest,\ self\)\._handle_exception\(exception\)
\ \ File\ "/opt/odoo/odoo15/odoo/odoo/http.py", line 301, in _handle_exception
raise exception.with_traceback(None) from new_cause
TypeError: 'NoneType' object is not subscriptable

Any idea why? Thank you.