button 'create_equipments' invisible in case to 'equipments_availables = True'

purchase.py

@@ -2,7 +2,7 @@
 #txhis repository contains the full copyright notices and license terms
 from trytond.pool import Pool, PoolMeta
 from trytond.model import ModelView, ModelSQL, fields
-from trytond.pyson import Eval
+from trytond.pyson import Eval, If, Bool
 from trytond.exceptions import UserError
 from trytond.i18n import gettext
 from .exceptions import (
@@ -18,14 +18,13 @@ class Purchase(metaclass=PoolMeta):
         super(Purchase, cls).__setup__()
         cls._buttons.update({
             'create_equipments': {
-                'invisible': ~Eval('equipment_avalaible')},
+                'invisible': If(Bool(Eval('equipment_available')), True)},
         })
 
-    
     @classmethod
     @ModelView.button
     def create_equipments(cls, purchases):
-        if len(purhcases) == 1:
+        if len(purchases) == 1:
             pool = Pool()
             Equipment = pool.get('optical_equipment.equipment')
             Line = pool.get('purchase.line')
@@ -33,7 +32,8 @@ class Purchase(metaclass=PoolMeta):
             purchase = purchases[0]
             
             for line in purchase.lines:
-                equipment = Equipment(
+                if line.product.equipment:
+                    equipment = Equipment(
                         company=line.company,
                         equipment_type=line.product.equipment_type,
                         party_address=line.address_equipment,
@@ -45,15 +45,20 @@ class Purchase(metaclass=PoolMeta):
                         refurbish=line.refurbish,
                         serial=line.serial_equipment,
                         software_version=line.product.software_version)
-
-                equipment.save()
+                    equipment.save()
+                else:
+                    continue
             purchase.equipment_available = True
             cls.save(purchases)
+            #raise UserError(str(purchase.equipment_available))
+
         else:
             raise InvalidNumberPurchases(
                 gettext('purchase.msg_invalid_number_purchases'))
 
             
+
+            
     """
     @classmethod
     @ModelView.button