Ensure that shipment work project is related to the same asset as the shipment

__init__.py

@@ -7,6 +7,7 @@ from .work import *
 def register():
     Pool.register(
         Project,
+        ShipmentWork,
         ContractLine,
         Contract,
         module='asset_work_project', type_='model')

work.py

@@ -1,13 +1,12 @@
 # The COPYRIGHT file at the top level of this repository contains the full
 # copyright notices and license terms.
-from collections import defaultdict
 from decimal import Decimal
 from trytond.model import fields
 from trytond.pool import Pool, PoolMeta
-from trytond.pyson import Eval
+from trytond.pyson import Eval, If, Bool
 
 
-__all___ = ['Project', 'ContractLine', 'Contract']
+__all___ = ['Project', 'ShipmentWork', 'ContractLine', 'Contract']
 __metaclass__ = PoolMeta
 
 
@@ -75,6 +74,18 @@ class Project:
         return res
 
 
+class ShipmentWork:
+    __name__ = 'shipment.work'
+
+    @classmethod
+    def __setup__(cls):
+        super(ShipmentWork, cls).__setup__()
+        if 'asset' not in cls.project.depends:
+            cls.project.domain.append(If(Bool(Eval('asset')),
+                    ('asset', '=', Eval('asset')), ()))
+            cls.project.depends.append('asset')
+
+
 class Contract:
     __name__ = 'contract'