Populating object problem

Question

User-1458727574 posted

I have a class that was generated from an XSD. The XML is very simple:

<Bills>
  <Bill>
    <Fileno/>
    <FileSuffix/>
    <Status/>
    <ErrorId/>
    <ErrorMessage/>
  </Bill>
</Bills>

There could be many Bill objects within Bills. The Bills class has only one property which is a List<> of Bill objects. The class is here:

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//     Runtime Version:4.0.30319.42000
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------

// 
// This source code was auto-generated by xsd, Version=4.6.1055.0.
// 
namespace ACLWebApi.ResponseClasses.BillingResponse
{
    using System.Collections.Generic;
    using System.Xml.Serialization;


    /// <remarks/>
    [System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "4.6.1055.0")]
    [System.SerializableAttribute()]
    [System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.ComponentModel.DesignerCategoryAttribute("code")]
    [System.Xml.Serialization.XmlTypeAttribute(AnonymousType = true)]
    [System.Xml.Serialization.XmlRootAttribute(Namespace = "", IsNullable = false)]
    public partial class Bills
    {

        private List<BillsBill> billField;

        /// <remarks/>
        [System.Xml.Serialization.XmlElementAttribute("Bill")]
        public List<BillsBill> Bill
        {
            get
            {
                return this.billField;
            }
            set
            {
                this.billField = value;
            }
        }
    }

    /// <remarks/>
    [System.CodeDom.Compiler.GeneratedCodeAttribute("xsd", "4.6.1055.0")]
    [System.SerializableAttribute()]
    [System.Diagnostics.DebuggerStepThroughAttribute()]
    [System.ComponentModel.DesignerCategoryAttribute("code")]
    [System.Xml.Serialization.XmlTypeAttribute(AnonymousType = true)]
    public partial class BillsBill
    {

        private string filenoField;

        private string fileSuffixField;

        private string statusField;

        private int errorIdField;

        private string errorMessageField;

        /// <remarks/>
        public string Fileno
        {
            get
            {
                return this.filenoField;
            }
            set
            {
                this.filenoField = value;
            }
        }

        /// <remarks/>
        public string FileSuffix
        {
            get
            {
                return this.fileSuffixField;
            }
            set
            {
                this.fileSuffixField = value;
            }
        }

        /// <remarks/>
        public string Status
        {
            get
            {
                return this.statusField;
            }
            set
            {
                this.statusField = value;
            }
        }

        /// <remarks/>
        [System.Xml.Serialization.XmlElementAttribute(DataType = "integer")]
        public int ErrorId
        {
            get
            {
                return this.errorIdField;
            }
            set
            {
                this.errorIdField = value;
            }
        }

        /// <remarks/>
        public string ErrorMessage
        {
            get
            {
                return this.errorMessageField;
            }
            set
            {
                this.errorMessageField = value;
            }
        }
    }
}

As I'm looping through the input data I build up a Bill each time.

billsBill.Fileno = billingData.fileNo.ToString();
billsBill.FileSuffix = billingData.suffix;
billsBill.Status = "error";
billsBill.ErrorId = statusNumber;
billsBill.ErrorMessage = sErrorString;

When I add the Bill to the Bills list it bombs out returning an Internal Server Error to the calling client. The error message is "

NullReferenceException: Object reference not set to an instance of an object."

The line of code that it bombs out on is:

bills.Bill.Add(billsBill);

Basically I want to add the Bill to the Bills list. Ultimately I have a function that serialises the Bills object to a string and returns it to the client but it doesn't allow me to add the Bill to the Bill list within Bills. What have I missed?