ERPNext create custom field on patch

from __future__ import unicode_literals
import frappe
from frappe.core.doctype.custom_field.custom_field import create_custom_field

def execute():
    opencart_extra_fields = {
        "Item": [{
            "label": "X Settings",
            "fieldname": "x_settings",
            "fieldtype": "Section Break",
            "insert_after": "add_image",
            "permlevel": 1
        }]
    }
    for dt, docfields in opencart_extra_fields.items():
        for df in docfields:
            df = frappe._dict(df)
            create_custom_field(dt, df)