minor fix

contract.py

@@ -170,3 +170,11 @@ class StaffContract(Workflow, ModelSQL, ModelView):
                 raise AccessError(gettext('staff.msg_employee_with_contract_current',
                                           contract=contracts_current[0].employee.rec_name))
         return super(StaffContract, cls).create(vlist)
+        
+    @classmethod
+    def delete(cls, records):
+        for contract in records:
+            if contract.number:
+                raise AccessError(gettext('staff.msg_dont_delete_contract',
+                                          contract=contracts_current[0].employee.rec_name))
+        return super(StaffContract, cls).delete(records)

message.xml

@@ -4,7 +4,10 @@ this repository contains the full copyright notices and license terms. -->
 <tryton>
     <data grouped="1">
         <record model="ir.message" id="msg_employee_with_contract_current">
-            <field name="text">The employee "%(contract)" already has a contract in draft or active!.</field>
+            <field name="text">The employee "%(contract)s" already has a contract in draft or active!.</field>
+        </record>
+        <record model="ir.message" id="msg_dont_delete_contract">
+            <field name="text">The contract for "%(contract)s" can not delete, cancel this.</field>
         </record>
         <record model="ir.message" id="msg_missing_contract_sequence">
             <field name="text">The contract sequence is missing on configuration!</field>