[FIX] hr_holidays: Add missing context check

Backport of ead3f03
Fixes #4341

addons/hr_holidays/hr_holidays.py

@@ -95,6 +95,8 @@ class hr_holidays_status(osv.osv):
     def name_get(self, cr, uid, ids, context=None):
         if not ids:
             return []
+        if context is None:
+            context = {}
 
         if not context.get('employee_id',False):
             # leave counts is based on empoyee_id, would be inaccurate if not based on correct employee