如果商机与条件不匹配，则显示所有商机，我们需要编辑这些商机

如何解决如果商机与条件不匹配，则显示所有商机，我们需要编辑这些商机

顶点类：

public class OppBasedOnStages {
    
        public Opportunity opp {get;set;}
        public List<Opportunity> opportunities {get;set;}
        public OppBasedonStages(ApexPages.StandardController controller) 
        {
            
        }
        
        public OppBasedOnStages() {
            opp = new Opportunity();
            opportunities = new List<Opportunity>();
        }
        
        public void showOpp() {
            if(opp.Id == null){
            if(opp.StageName == 'Prospecting'){
                opportunities = [SELECT Id,Name,StageName,Amount FROM Opportunity WHERE StageName='Prospecting'];
            }
            else if(opp.StageName == 'Qualification'){
                opportunities = [SELECT Id,Amount FROM Opportunity WHERE StageName='Qualification'];
            }
            else if(opp.StageName == 'Need Analysis'){
                opportunities = [SELECT Id,Amount FROM Opportunity WHERE StageName='Need Analysis'];
            }
            else if(opp.StageName == 'Need Analysis'){
                opportunities = [SELECT Id,Amount FROM Opportunity WHERE StageName='Need Analysis'];
            }
            else if(opp.StageName == 'Negotiation/Review'){
                opportunities = [SELECT Id,Amount FROM Opportunity WHERE StageName='Negotiation/Review'];
            }
            else if(opp.StageName == 'perception Analysis'){
                opportunities = [SELECT Id,Amount FROM Opportunity WHERE StageName='perception Analysis'];
            }
            else
            {
                ApexPages.Message Myerrormsg = new ApexPages.Message(ApexPages.Severity.INFO,' No opportunities exist with this stagename.' + Opp.StageName);
                ApexPages.addMessage(Myerrormsg);
            }
        }
        }
    }

Visualforce页面：

<apex:page StandardController = "Opportunity" extensions = "OppBasedonStages" >
 <apex:form >
        <apex:pageBlock >
            <apex:pageBlockSection >
                <apex:inputField value="{!opp.StageName}" >
                    <apex:commandButton value="display" Action="{!showOpp}"/>
                    <apex:actionSupport event="onchange" action="{!showOpp}" reRender="display"/>
                </apex:inputField>
            </apex:pageBlockSection>
            <apex:pageBlockTable value="{!opportunities}" var="a">
                <apex:column value="{!a.Name}" />
                <apex:column value="{!a.StageName}" />
                <apex:column value="{!a.Amount}"/>
            </apex:pageBlockTable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

我遇到了运行时错误，因此我想清除它。是该平台的新手。请帮助我清除此错误。谢谢。 错误：尝试取消引用空对象 页面oppbasedonstagesvf中的表达式'{！showOpp}'中存在错误：Class.OppBasedOnStages.showOpp：第16行，第1列