Hello, 

This is my Trigger and I am receiving an error when I am editing a Record:

trigger Eisai_Send_Email_Notification_End_Of_Fiscal_Year on PTO_esi__c(after update){
    List<String> sendToRep_List = new List<String>();
    List<String> sendToDM_List = new List<String>();
    String emailTemplateIdRep = [SELECT Id FROM EmailTemplate WHERE DeveloperName = 'Email_Template_PTO_Year_End_Notification_Rep'].Id;
    String emailTemplateIdDM = [SELECT Id FROM EmailTemplate WHERE DeveloperName = 'Email_Template_PTO_Year_End_Notification_DM'].Id;
    
    for(PTO_esi__c tpto: [SELECT Owner_Email__c,ID FROM PTO_esi__c WHERE Type_of_User__c = 'REP'])
        {
        sendToRep_List.add(tpto.Owner_Email__c);
        }
    for(PTO_esi__c tpto: [SELECT Owner_Email__c,ID FROM PTO_esi__c WHERE Type_of_User__c = 'DM'])
        {
        sendToDM_List.add(tpto.Owner_Email__c);
        }
    
    for(PTO_esi__c pto: trigger.new){
        
        if(pto.Active__c && pto.Current_user_Level__c == 'REP')
            {
            Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
            mail.setToAddresses(sendToRep_List);
            mail.setTemplateId(emailTemplateIdRep);
            Messaging.sendEmail(new Messaging.SingleEmailMessage[]{ mail });
            }
            
        if(pto.Active__c && pto.Current_user_Level__c == 'DM')
            {
            Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
            mail.setToAddresses(sendToDM_List);
            mail.setTemplateId(emailTemplateIdDM);
            Messaging.sendEmail(new Messaging.SingleEmailMessage[]{ mail });
            }
    }

}




ERROR Message: 
Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger Eisai_Send_Email_Notification_End_Of_Fiscal_Year caused an unexpected exception, contact your administrator: Eisai_Send_Email_Notification_End_Of_Fiscal_Year: execution of AfterUpdate caused by: System.EmailException: SendEmail failed. First exception on row 0; first error: REQUIRED_FIELD_MISSING, Missing targetObjectId with template: []: Trigger.Eisai_Send_Email_Notification_End_Of_Fiscal_Year: line 31, column 1

I am editing a record with value on this field (Current_user_Level__c ) = DM
and setting Active checkbox to true. 

Thank you.