Use IgnoreNamspace to stop recursive serialization, e.g.

    var ss = new StateSerializer();
    ss.IgnoreNamspace("System.Xml");

Example

var ss = new StateSerializer();
ss.IgnoreNamspace("System.Xml");

var str = ss.ToXml(new MyClass());
Console.WriteLine(str);


    class MyBaseClass : XmlDocument
    {
        protected string[] arrStrings = new string[] { "a", "b", "c" };
    }

    class MyClass : MyBaseClass
    {
        static DateTime date = DateTime.Now;
        private Type myTypeField = typeof(string);
        public XmlDocument[] arrayXml;
        public int Id { get; set; } = 1;
        public MyClass SelfReference { get; set; }
        public object NullReference { get; set; }
        public MyClass()
        {
            var xml = new XmlDocument();

            this.SelfReference = this;
            this.arrayXml = new XmlDocument[] { xml, xml, null };
        }
    }

output

    <?xml version="1.0" encoding="utf-16"?>
    <Root Type="MyClass" Id="1">
      <IdkBackingField Type="Int32">1</IdkBackingField>
      <NullReferencekBackingField Type="Object" />
      <SelfReferencekBackingField Type="MyClass" Id="1" HasBeenSerializedBefore="true" />
      <arrayXml Type="XmlDocument[]" Id="2">
        <item Type="XmlDocument" Id="3">System.Xml.XmlDocument</item>
        <item Type="XmlDocument" Id="3">System.Xml.XmlDocument</item>
        <item />
      </arrayXml>
      <arrStrings Type="String[]" Id="4">
        <item Type="String">a</item>
        <item Type="String">b</item>
        <item Type="String">c</item>
      </arrStrings>
      <date Type="DateTime">13-07-2017 10:39:44</date>
      <myTypeField Type="Type" Id="5">System.String</myTypeField>
    </Root>