public class sendPanEmail {

    public String subject { get; set; }
    public String body { get; set; }
    private final Panel__c panel;

    public sendPanEmail() {
        panel = [SELECT Name,(SELECT Name,Panelists_Email__c FROM Panelists__r) FROM Panel__c
        WHERE Id IN (Select Assigned_to_Panel__c FROM Opportunity WHERE Id= :ApexPages.currentPage().getParameters().get('id'))];
    }

    public Panel__c getPanelist() {
        return panel;
    }

    public PageReference send() {

        Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
        String addresses;

        if (panel.Assigned_to_Panel__r.Panelists[0].Panelists_Email__c != null) {
            addresses = panel.Assigned_to_Panel__r.Panelists[0].Panelists_Email__c;
            for (Integer i = 1; i < panel.Assigned_to_Panel__r.Panelists.size(); i++)
            {
                if (panel.Assigned_to_Panel__r.Panelists[i].Panelists_Email__c != null)
                {
                    addresses += ':' + panel.Assigned_to_Panel__r.Panelists[i].Panelists_Email__c;
                }
            }
        }

        String[] toAddresses = addresses.split(':', 0);

        email.setSubject( subject );
        email.setToAddresses( toAddresses );
        email.setPlainTextBody( body );

        Messaging.SendEmailResult [] r = Messaging.sendEmail(new Messaging.SingleEmailMessage[] {email});

        PageReference pageRef = ApexPages.currentPage();
        pageRef.setRedirect(true);
        return pageRef;
    }
}