```
trigger OpportunityAmount on Opportunity (before insert) {

    List<String> stage=new List<String>();
    For(Opportunity opp:Trigger.New){
        stage.add(opp.StageName);
    }
    List<Opportunity> stageopp=[select StageName from Opportunity where StageName=:stage];
     if(stageopp.StageName =='Closed won'){////<---- Error
        for(Opportunity opp:Trigger.New){
            opp.addError('Amount field is a required field');
        }
    }

}

```

While saving above trigger, i am getting following. Please help me in this.

> 
> Initial term of field expression must be a concrete SObject:
>  List
> 
> 
>