I'm trying to replace a field in the product.template view with a field of my own. Following the suggestions in the book https://www.amazon.co.uk/Odoo-Development-Essentials-Daniel-Reis-ebook/dp/B01KI1F302/ref=sr_1_1?ie=UTF8&qid=1507024599&sr=8-1&keywords=odoo+10+development+essentials , I've created the following xml in views/views.xml - 

<odoo>

  <data>

    <record model="ir.ui.view" id="view_product_template_form_inherited">                                                                                                                                                                                                                                                                                               

      <field name="name">MSUK view product template form</field>

      <field name="model">product.template</field>

      <field name="inherit_id" ref="product.product_template_only_form_view" />

      <field name="arch" type="xml">

          <xpath name="//field[@name='project_id']" position="before">

            <field name="project_templates" />

          </xpath>     

      </field>

    </record>

  </data>

</odoo>

and in models.py:
from odoo import models, fields, api
from pprint import pprint
import logging 
class msuk_sales(models.Model):
    _inherit = 'product.template'
    logger = logging.getLogger()
    project_templates = fields.Char('Templates', required=True) #String("template projects") #Many2one('project_project')                                                                                                                                                                                                                                               
    # for record in project_templates:
        # logger.log(20, record)

My module is available when I click "Apps", so I'll not bother showing you the __manifest__.py

when I click "Upgrade", I get the following stacktrace:

Can anyone help? I've been stuck on this for two days, or more, now!!

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 640, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 677, in dispatch
    result = self._call_function(**self.params)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 333, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/service/model.py", line 101, in wrapper
    return f(dbname, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 326, in checked_call
    result = self.endpoint(*a, **kw)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 935, in __call__
    return self.method(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/odoo/http.py", line 506, in response_wrap
    response = f(*args, **kw)
  File "/usr/lib/python2.7/dist-packages/odoo/addons/web/controllers/main.py", line 889, in call_button
    action = self._call_kw(model, method, args, {})
  File "/usr/lib/python2.7/dist-packages/odoo/addons/web/controllers/main.py", line 877, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/api.py", line 681, in call_kw
    return call_kw_multi(method, model, args, kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/api.py", line 672, in call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/odoo/addons/base/module/module.py", line 527, in button_immediate_upgrade
    return self._button_immediate_function(type(self).button_upgrade)
  File "/usr/lib/python2.7/dist-packages/odoo/addons/base/module/module.py", line 484, in _button_immediate_function
    modules.registry.Registry.new(self._cr.dbname, update_module=True)
  File "/usr/lib/python2.7/dist-packages/odoo/modules/registry.py", line 82, in new
    odoo.modules.load_modules(registry._db, force_demo, status, update_module)
  File "/usr/lib/python2.7/dist-packages/odoo/modules/loading.py", line 335, in load_modules
    force, status, report, loaded_modules, update_module)
  File "/usr/lib/python2.7/dist-packages/odoo/modules/loading.py", line 237, in load_marked_modules
    loaded, processed = load_module_graph(cr, graph, progressdict, report=report, skip_modules=loaded_modules, perform_checks=perform_checks)
  File "/usr/lib/python2.7/dist-packages/odoo/modules/loading.py", line 156, in load_module_graph
    _load_data(cr, module_name, idref, mode, kind='data')
  File "/usr/lib/python2.7/dist-packages/odoo/modules/loading.py", line 95, in _load_data
    tools.convert_file(cr, module_name, filename, idref, mode, noupdate, kind, report)
  File "/usr/lib/python2.7/dist-packages/odoo/tools/convert.py", line 845, in convert_file
    convert_xml_import(cr, module, fp, idref, mode, noupdate, report)
  File "/usr/lib/python2.7/dist-packages/odoo/tools/convert.py", line 915, in convert_xml_import
    obj.parse(doc.getroot(), mode=mode)
  File "/usr/lib/python2.7/dist-packages/odoo/tools/convert.py", line 796, in parse
    self.parse(rec, mode)
  File "/usr/lib/python2.7/dist-packages/odoo/tools/convert.py", line 799, in parse
    self._tags[rec.tag](rec, de, mode=mode)
  File "/usr/lib/python2.7/dist-packages/odoo/tools/convert.py", line 707, in _tag_record
    id = self.env(context=rec_context)['ir.model.data']._update(rec_model, self.module, res, rec_id or False, not self.isnoupdate(data_node), noupdate=self.isnoupdate(data_node), mode=self.mode)
  File "/usr/lib/python2.7/dist-packages/odoo/addons/base/ir/ir_model.py", line 1228, in _update
    record = record.create(values)
  File "/usr/lib/python2.7/dist-packages/odoo/addons/base/ir/ir_ui_view.py", line 363, in create
    return super(View, self).create(self._compute_defaults(values))
  File "/usr/lib/python2.7/dist-packages/odoo/models.py", line 3839, in create
    self._fields[key].determine_inverse(record)
  File "/usr/lib/python2.7/dist-packages/odoo/fields.py", line 1000, in determine_inverse
    getattr(records, self.inverse)()
  File "/usr/lib/python2.7/dist-packages/odoo/addons/base/ir/ir_ui_view.py", line 220, in _inverse_arch
    view.write(data)
  File "/usr/lib/python2.7/dist-packages/odoo/addons/base/ir/ir_ui_view.py", line 381, in write
    return super(View, self).write(self._compute_defaults(vals))
  File "/usr/lib/python2.7/dist-packages/odoo/models.py", line 3564, in write
    self._write(old_vals)
  File "/usr/lib/python2.7/dist-packages/odoo/models.py", line 3716, in _write
    self._validate_fields(vals)
  File "/usr/lib/python2.7/dist-packages/odoo/models.py", line 1083, in _validate_fields
    raise ValidationError("%s\n\n%s" % (_("Error while validating constraint"), tools.ustr(e)))
ParseError: "Error while validating constraint

Argument must be bytes or unicode, got 'NoneType'
None" while parsing /home/dominic.pain/miningsearchesuk/src/python/msuk_sales/views/views.xml:3, near
<record model="ir.ui.view" id="view_product_template_form_inherited">
      <field name="name">MSUK view product template form</field>
      <field name="model">product.template</field>
      <field name="inherit_id" ref="product.product_template_only_form_view"/>
      <field name="arch" type="xml">
          <xpath name="//field[@name='project_id']" position="before">
            <field name="project_templates"/>
          </xpath>
      </field>
    </record>