I keep getting keyError for values in api.depends

here is the traceback:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/werkzeug/serving.py", line 177, in run_wsgi
    execute(self.server.app)
  File "/usr/lib/python2.7/dist-packages/werkzeug/serving.py", line 165, in execute
    application_iter = app(environ, start_response)
  File "/opt/odoo8/odoo/openerp/service/server.py", line 290, in app
    return self.app(e, s)
  File "/opt/odoo8/odoo/openerp/service/wsgi_server.py", line 216, in application
    return application_unproxied(environ, start_response)
  File "/opt/odoo8/odoo/openerp/service/wsgi_server.py", line 202, in application_unproxied
    result = handler(environ, start_response)
  File "/opt/odoo8/odoo/openerp/http.py", line 1290, in __call__
    return self.dispatch(environ, start_response)
  File "/opt/odoo8/odoo/openerp/http.py", line 1264, in __call__
    return self.app(environ, start_wrapped)
  File "/usr/lib/python2.7/dist-packages/werkzeug/wsgi.py", line 579, in __call__
    return self.app(environ, start_response)
  File "/opt/odoo8/odoo/openerp/http.py", line 1426, in dispatch
    ir_http = request.registry['ir.http']
  File "/opt/odoo8/odoo/openerp/http.py", line 346, in registry
    return openerp.modules.registry.RegistryManager.get(self.db) if self.db else None
  File "/opt/odoo8/odoo/openerp/modules/registry.py", line 339, in get
    update_module)
  File "/opt/odoo8/odoo/openerp/modules/registry.py", line 370, in new
    openerp.modules.load_modules(registry._db, force_demo, status, update_module)
  File "/opt/odoo8/odoo/openerp/modules/loading.py", line 357, in load_modules
    registry.setup_models(cr)
  File "/opt/odoo8/odoo/openerp/modules/registry.py", line 197, in setup_models
    model._setup_complete(cr, SUPERUSER_ID)
  File "/opt/odoo8/odoo/openerp/api.py", line 241, in wrapper
    return old_api(self, *args, **kwargs)
  File "/opt/odoo8/odoo/openerp/api.py", line 336, in old_api
    result = method(recs, *args, **kwargs)
  File "/opt/odoo8/odoo/openerp/models.py", line 3023, in _setup_complete
    field.setup_triggers(self.env)
  File "/opt/odoo8/odoo/openerp/fields.py", line 593, in setup_triggers
    self._setup_dependency([], model, path.split('.'))
  File "/opt/odoo8/odoo/openerp/fields.py", line 607, in _setup_dependency
    fields = [model._fields[head]]
KeyError: 'hr_employee' 

here is my code:

lateform.py

class late_form(osv.Model):
	_name = "late.form"
	_columns = {
		'name': fields.char('Label',required=True,size=32),
		'user_id': fields.many2one('hr.employee', 'Name', required=True),
		'date': fields.datetime('Date & Time',required=True),
		'reason': fields.text('Reason'),
		'employee_id': fields.one2many('late.form','user_id'),
		'state': fields.selection([('invalid', 'Invalid'),
					   ('valid', 'Valid')]),
	}
	_defaults = {
		'name': "Late report",
		'date': fields.datetime.now,
		'state': 'invalid',
	}

	def set_invalid(self, cr, uid, ids, context=None):
		return self.write(cr, uid, ids, {'state': 'invalid'}, context=context)

	def set_valid(self, cr, uid, ids, context=None):
		return self.write(cr, uid, ids, {'state': 'valid'}, context=context)

	def _send_user_id(self, cr, uid, context=None):
		""" Returns ID of user
		"""
		if context is None:
			context = {}
		return {'user_id': self.browse(cr, uid, employee_id, context=context)}

class hr_employee(models.Model):
	_inherit = 'hr_employee'

	#what will trigger this functional field
	@api.one
	#events which will decide when this functional field will be updated
	#when an id is added, or when the state of a sale_order_id is changed, e.g. from draft to confirmed
	@api.depends('hr.employee')
	def compute_late_mtd(self):
		cursor = self._cr
		user = self._uid
		#loop through all employees in the view
		for employee in self:
			#define starting date and time
			today = datetime.datetime.today()
			#define them as strings just in case
			start_date = str(today.replace(day=1).strftime('%m/%d/%Y'))
			next_month = today.replace(day=28) + datetime.timedelta(days=4)
			end_date = str(next_month - datetime.timedelta(days=next_month.day))
			print end_date

			#references the model we need to work with
			employee_obj = self.pool.get('late.form')
			#narrowing down and selecting all the relevant instances with specific domains
			#this search returns an array
			late_times = employee_obj.search(cursor, user, [('date','>=',start_date),('date','<=',end_date),('user_id','=',user.id),('state','=','valid')])
			print late_times
			
			total = 0.0
			for late.form in employee_obj.browse(cursor, user, late_times):
				total += 1
			hr.employee.late_mtd = total
	
	#run the function defined above and insert into a float field named late_mtd

	_columns = {
		'late_mtd': fields.float(compute='compute_late_mtd', store=False, string='Times late this month'),
	}