Hi, 
 Im getting the following error and cannot figure out why: 

System.EmailException: SendEmail failed. First exception on row 0; first error: INVALID_EMAIL_ADDRESS, Email address is invalid: null: [toAddresses, null]

Class.email_class.send: line 48, column 1
Class.TestquoteEmailclass.sendEmailTestMethod: line 47, column 1

Below is my test class: 

@isTest
public class TestquoteEmailclass {
    @isTest static void sendEmailTestMethod(){
    
        Product2 prod = new Product2(Name = 'SLA: Bronze', IsActive = true);
        insert prod;
        PricebookEntry pbe=new PricebookEntry(unitprice=0.01,Product2Id=prod.Id, Pricebook2Id=Test.getStandardPricebookId(), IsActive= true); 
        insert pbe; 
        Account acc = new Account (name='Acme');
        insert acc;
        Opportunity opp= new Opportunity (name='Testopp', Accountid=acc.id, CloseDate= date.today(), StageName='Closed Won', Pricebook2id=Test.getStandardPricebookId());
        insert opp; 
        OpportunityLineItem oppLine = new OpportunityLineItem( pricebookentryid=pbe.Id,TotalPrice=2000, Quantity = 2,Opportunityid = opp.Id);
        insert oppLine;       
        Quote q= new Quote (Name='Testq', Opportunityid=opp.id, QuotetoInvoice__c= True,  Pricebook2id=Test.getStandardPricebookId());
        insert q;
    
     System.currentPagereference().getParameters().put('id',q.id);
     Attachment objAtt = new Attachment();
     objAtt.Name = 'Test';
     objAtt.body = Blob.valueof('string');
     objAtt.ParentId = q.Id;
     insert objAtt;

         ApexPages.StandardController sc =new ApexPages.StandardController(q); 
        email_class ec=new email_class (sc);
        ec.ToAddresses='test@gmail.com';
         ec.CCAddresses='test2@gmail.com';
        ec.emailCC= 'test3@gmail.com';
        ec.email_body='test1111111';
        ec.subject='test22222';
        
         Messaging.InboundEmail email = new Messaging.InboundEmail();  
         Messaging.InboundEnvelope env = new Messaging.InboundEnvelope();
        email.plainTextBody = 'This should become a note';
        email.fromAddress ='test@test.com';
        String contactEmail = 'jsmith@salesforce.com';
        email.ccAddresses = new String[] {'Jon Smith <' + contactEmail + '>'};
        email.subject = 'Dummy Account Name 123';

        ec.send();

}
}

And my controller:

public class email_class{
        
    Public string ToAddresses {get;set;}
    Public string CCAddresses {get;set;}
    Public string quoteId {get;set;}
    Public string subject {get;set;}
    public string email_body {get;set;}
    public string emailTo {get;set;}
    public string emailCC {get;set;}
     public  string [] ccaddress;   
              
        
        
        public email_class(ApexPages.StandardController controller) {
                quoteId = ApexPages.currentPage().getParameters().get('id');
    }
        
    Public PageReference send(){

                Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage(); // set the to address
                mail.setToAddresses(new String[] {emailTo}); 
               // mail.setCCAddresses(new String[] {emailCC});   //set the cc address
                   
        if(emailCC != null && emailCC.trim() != '')
        {
        ccaddress = emailCC.split(',',0);
        mail.setCCAddresses(ccaddress);}
                                                              
   
                mail.setSubject(subject);
                mail.setBccSender(false);
                mail.setUseSignature(false);
                mail.setPlainTextBody(email_body);
               

                List<Messaging.Emailfileattachment> fileAttachments = new List<Messaging.Emailfileattachment>();

                for (Attachment a : [select Name, Body, BodyLength from Attachment where ParentId = :quoteId]){  // Add to attachment file list  
                        Messaging.Emailfileattachment efa = new Messaging.Emailfileattachment();  
                        efa.setFileName(a.Name); 
                        efa.setBody(a.Body); 
                        fileAttachments.add(efa);
                }
                mail.setFileAttachments(fileAttachments);// Send email
                Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
                return null;
        }
}

Any help is appreciated !