[Bug] [Develop] AttributeError: 'Meta' object has no attribute 'nsm_parent_field'

[Alchez]

@netchampfaris After the addition in #8312, bench update breaks at migration (documented at frappe/erpnext#18893). I made the fix proposed at #8328, but now I get the following error (also added in #8312):

Executing erpnext.patches.v12_0.add_default_dashboards in erpn.v13 (_89ee9ce4255b7d4f)
Traceback (most recent call last):
  File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/utils/bench_helper.py", line 97, in <module>
    main()
  File "/home/rohan/erpn-edge/apps/frappe/frappe/utils/bench_helper.py", line 18, in main
    click.Group(commands=commands)(prog_name='bench')
  File "/home/rohan/erpn-edge/env/lib/python3.6/site-packages/click/core.py", line 764, in __call__
    return self.main(*args, **kwargs)
  File "/home/rohan/erpn-edge/env/lib/python3.6/site-packages/click/core.py", line 717, in main
    rv = self.invoke(ctx)
  File "/home/rohan/erpn-edge/env/lib/python3.6/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/rohan/erpn-edge/env/lib/python3.6/site-packages/click/core.py", line 1137, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/rohan/erpn-edge/env/lib/python3.6/site-packages/click/core.py", line 956, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/rohan/erpn-edge/env/lib/python3.6/site-packages/click/core.py", line 555, in invoke
    return callback(*args, **kwargs)
  File "/home/rohan/erpn-edge/env/lib/python3.6/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/commands/__init__.py", line 25, in _func
    ret = f(frappe._dict(ctx.obj), *args, **kwargs)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/commands/site.py", line 233, in migrate
    migrate(context.verbose, rebuild_website=rebuild_website, skip_failing=skip_failing)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/migrate.py", line 48, in migrate
    frappe.modules.patch_handler.run_all(skip_failing)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/modules/patch_handler.py", line 41, in run_all
    run_patch(patch)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/modules/patch_handler.py", line 30, in run_patch
    if not run_single(patchmodule = patch):
  File "/home/rohan/erpn-edge/apps/frappe/frappe/modules/patch_handler.py", line 71, in run_single
    return execute_patch(patchmodule, method, methodargs)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/modules/patch_handler.py", line 91, in execute_patch
    frappe.get_attr(patchmodule.split()[0] + ".execute")()
  File "/home/rohan/erpn-edge/apps/erpnext/erpnext/patches/v12_0/add_default_dashboards.py", line 8, in execute
    add_dashboards()
  File "/home/rohan/erpn-edge/apps/erpnext/erpnext/setup/setup_wizard/operations/install_fixtures.py", line 505, in add_dashboards
    dashboard_data = get_default_dashboards()
  File "/home/rohan/erpn-edge/apps/erpnext/erpnext/setup/setup_wizard/data/dashboard_charts.py", line 7, in get_default_dashboards
    company = frappe.get_doc("Company", frappe.defaults.get_defaults().company)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/__init__.py", line 734, in get_doc
    doc = frappe.model.document.get_doc(*args, **kwargs)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/model/document.py", line 69, in get_doc
    return controller(*args, **kwargs)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/model/document.py", line 104, in __init__
    self.load_from_db()
  File "/home/rohan/erpn-edge/apps/frappe/frappe/model/document.py", line 149, in load_from_db
    super(Document, self).__init__(d)
  File "/home/rohan/erpn-edge/apps/frappe/frappe/model/base_document.py", line 72, in __init__
    self.__setup__()
  File "/home/rohan/erpn-edge/apps/frappe/frappe/utils/nestedset.py", line 187, in __setup__
    if self.meta.nsm_parent_field:
AttributeError: 'Meta' object has no attribute 'nsm_parent_field'