NullReferenceException while saving XML File with Linq - winforms

Question

I keep getting a NullReferenceException at this line UserRoot.Element("User_ID").Value = User.User_ID.ToString();
What exactly am I doing wrong?
Here's the majority of the code for that method
if (File.Exists(Path2UserDB + User.User_ID.ToString() + ".db") == false)
{
File.Create(Path2UserDB + User.User_ID.ToString() + ".db");
}
XElement UserRoot = new XElement("User");
UserRoot.Element("User_ID").Value = User.User_ID.ToString();
UserRoot.Element("Full_Name").Value = User.Full_Name;
UserRoot.Element("Gender").Value = User.Gender;
UserRoot.Element("BirthDate").Value = User.BirthDate.ToString();
UserRoot.Element("PersonType").Value = User.PersonType.ToString();
UserRoot.Element("Username").Value = User.Username;
UserRoot.Element("Password").Value = User.Password;
UserRoot.Element("Email_adddress").Value = User.Email_Address;
XDocument UserDoc = new XDocument();
UserDoc.Save(Path2UserDB + User.User_ID.ToString() + ".db");
Thanks
I know that saving Usernames and Passwords in plain text is incredibly unsafe, but this is only going to be accessed by one process that I will eventually implement strong security

Answer 1

The Element("User_ID") method returns an existing element named <User_ID>, if any.
Since your XML element is empty, it returns null.
You should create your XML like this:
var userDoc = new XDocument(
new XElement("User",
new XElement("User_ID", User.User_ID),
new XElement("Full_Name", User.Full_Name),
new XElement("Gender", User.Gender),
...
)
);
Alternatively, you can call the Add method to add a node to an existing element.

Answer 2

You are getting this error, because there is no XML element called User_ID under UserRoot to set its value. If you comment it out, you will get the same error on the next line and so on for every other Element, since you haven't added Elements with thos names. To create the tree that you want, try this:
XElement UserRoot =
new XElement("User",
new XElement("User_ID", User.User_ID.ToString()),
new XElement("Full_Name", User.Full_Name),
new XElement("Gender", User.Gender),
new XElement("BirthDate", User.BirthDate.ToString()),
new XElement("PersonType", User.PersonType.ToString()),
new XElement("Username", User.Username),
new XElement("Password", User.Password),
new XElement("Email_adddress", User.Email_Address)
);
The following MSDN link on XML Tree Creation with XElement will be of help.

Answer 3

You want to check if the value is null or empty before running methods on it.
if(!String.IsnullorEmpty(User.User_ID))
UserRoot.Element("User_ID").Value = User.User_ID.ToString();