Microsoft Graph API issue when no cc or bcc recipients

Constructing Email Message using REST and C# - Invalid recipients I am reasonably new to C#, but not .NET development. I am also fairly new to Graph development.

I am trying to build the code that can be used to construct messages within my organisation. Ultimately the code will become an RPA code object.

I have a class for the message, which has classes defined for toRecipient, ccRecipient and bccRecipient. Creating and sending an email works fine when I have data for the To, CC and Bcc options. However, I get an error message if I only have To recipients and not cc or Bcc recipitents. Similarly I cannot send to bcc only, as the code is looking for values to the toRecipients and CC recipients.

Error message:

{
    "error":{
        "code":"ErrorInvalidRecipients",
        "message":"At least one recipient isn't valid., Recipient '' is not resolved. All recipients must be resolved before a message can be submitted."
    }
}

How do I make the sub classes for cc and BCC optional? – or is there syntax I can use to tell the API that cc and bcc fields are empty?

I build the class based on a message created using Postman, and then using Paste Special into my message class.

Class:

public class gMessage {
    public grfMessage message { get; set; }
    public string saveToSentItems { get; set; }
}

public class grfMessage {
    public string subject { get; set; }
    public Body body { get; set; }
    public List <ToRecipient> toRecipients { get; set; }
    public List<ToRecipient> ccRecipients { get; set; }
    public List<ToRecipient> bccRecipients { get; set; }
}

public class Body {
    public string contentType { get; set; }
    public string content { get; set; }
}

public class ToRecipient {
    public EmailAddress EmailAddress { get; set; }
    public static implicit operator List<object>(ToRecipient v) {
        throw new NotImplementedException();
    }
}

public class EmailAddress {
    public string address { get; set; }
}

Input variables:

public static string EmailRecipients = "email1@company.com";email2@company.com;
public static string EmailCCList = "email3@organisation.org";
public static string EmailBCCList = "";

Code to build message:

// Define our recipient list 
List<ToRecipient> listRecip = new List<ToRecipient>(); // define new list. We will ultimately split the inbount array into this list
ToRecipient RecipEmail;
EmailAddress ema1;

// now split our list of recipients to an array
string[] ToAdds = EmailRecipients.Split(';');
foreach (var email in ToAdds) {
    // Build the recipients list first
    RecipEmail = new ToRecipient();
    ema1 = new EmailAddress {
        address = email
    }; // Email Address class contains Address
    RecipEmail.EmailAddress = ema1;
    listRecip.Add(RecipEmail); // We have now added to the list in memory
}

//Define our CC List
List<ToRecipient> ccRecip = new List<ToRecipient>(); // define new list. We will ultimately split the inbount array into this list
ToRecipient ccEmail;

string[] ccAdds = EmailCCList.Split(';');
foreach (var email in ccAdds) {
    // Build the recipients list first
    ccEmail = new ToRecipient();
    ema1 = new EmailAddress {
        address = email
    }; // Email Address class contains Address
    ccEmail.EmailAddress = ema1;
    ccRecip.Add(ccEmail); // We have now added to the list in memory
}

//Define our BCC List
List<ToRecipient> bccRecip = new List<ToRecipient>(); // define new list. We will ultimately split the inbount array into this list
ToRecipient bccEmail;

string[] bccAdds = EmailBCCList.Split(';');
foreach (var email in bccAdds) {
    // Build the recipients list first
    bccEmail = new ToRecipient();
    ema1 = new EmailAddress {
        address = email
    }; // Email Address class contains Address
    bccEmail.EmailAddress = ema1;
    bccRecip.Add(bccEmail); // We have now added to the list in memory
}


var msgData = new gMessage() {
    message = new grfMessage() {
        subject = mSubject,
        body = new Body() {
            contentType = mContentType,
            content = mBody
        },
        toRecipients = listRecip,
        ccRecipients = ccRecip,
        bccRecipients = bccRecip
    },
    saveToSentItems = "True"
};