Customizing naming series for a doctype

Hello,

I created a new doctype in ERPNext call Equipment for manufacturing process in order to monitor the capacity of our suppliers. And I want to autoname it by a machine type code and supplier id.

I followed the instruction in this discussion: Customizing naming series.

I add the following block within doc_events = {…}

"Equipment": {
	   "autoname": "erpnext.hooked_autoname.equipment_autoname"
}

And I created a python file called hooked_autoname.py in the same folder where hooks.py is.

from frappe.model.naming import make_autoname
def equipment_autoname(doc, method):
	doc.name = make_autoname(doc.equipment_type + doc.supplier)

After I reload the page and save a new equipment I got the error message.

App dotted is not installed

Which step did I miss? Thanks for your help.