i have code like this

def _picking_assign(self,cr, uid, move_ids, procurement_group, location_from, location_to, context=None):
    pick_obj = self.pool.get("stock.picking")        
    move = self.browse(cr,uid,move_ids[0])        
    obj_model = self.pool.get('ir.model')        
    obj_model_id = obj_model.search(cr,uid,[ ('model','=',move.procurement_id.sale_line_id.order_id.__class__.__name__) ])                
    if move.cabang:
        values = {                
            'origin': move.origin,                
            'company_id': move.company_id and move.company_id.id or False,                
            'move_type': move.group_id and move.group_id.move_type or 'direct',                
            'partner_id': move.partner_id.id or False,                
            'picking_type_id': move.picking_type_id and move.picking_type_id.id or False,                
            'group_id': procurement_group,                
            'location_id':location_from,                
            'location_dest_id': location_to,                
            'cabang': move.cabang.id,                
            'state': 'draft',                
            'transaction_id': move.procurement_id.sale_line_id.order_id.id,                
            'model_id': obj_model_id[0]            
            }            
        pick = pick_obj.create(cr, uid, values, context=context)            
        self.write(cr, uid, move_ids, {'picking_id': pick}, context=context)                    
    res = super(stock,self)._picking_assign(cr, uid, move_ids, procurement_group, location_from, location_to, context=context)        
    pick_obj.force_assign(cr,uid,pick)        
    return res

but i getting error like this

File "/home/susi/odoo/addons/SAVIRA/mcs_sale_order/mcs_procurement_order.py", line 28, in_picking_assign    pick_obj.force_assign(cr,uid,pick)ValueError: "local variable 'pick' referenced before assignment" while evaluatingu'action_ship_create()'

anyone can help me what its mean? and how i fix it. Thanks before