Integer, Numeric and Float allow None as value

NULL value is None and not False

issue2022
review237004

service.py

@@ -1,5 +1,6 @@
 #This file is part of Tryton.  The COPYRIGHT file at the top level of
 #this repository contains the full copyright notices and license terms.
+from decimal import Decimal
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.model.cacheable import Cacheable
 from trytond.pyson import Eval
@@ -106,6 +107,9 @@ class EmployeeCostPrice(ModelSQL, ModelView):
         ]
         self._order.insert(0, ('date', 'DESC'))
 
+    def default_cost_price(self):
+        return Decimal(0)
+
     def default_date(self):
         date_obj = Pool().get('ir.date')
         return date_obj.today()

work.py

@@ -42,6 +42,7 @@ class Work(ModelSQL, ModelView):
         digits=(16, Eval('currency_digits', 2)),
         states={
             'invisible': Eval('type') != 'task',
+            'required': Eval('type') == 'task',
             }, depends=['type', 'currency_digits'])
     revenue = fields.Function(fields.Numeric('Revenue',
             digits=(16, Eval('currency_digits', 2)),