Suppress Null Value Types from Being Emitted by XmlSerializer

Try adding:

public bool ShouldSerializeAmount() {
   return Amount != null;
}

There are a number of patterns recognised by parts of the framework. For info, XmlSerializer also looks for public bool AmountSpecified {get;set;}.

Full example (also switching to decimal):

using System;
using System.Xml.Serialization;

public class Data {
    public decimal? Amount { get; set; }
    public bool ShouldSerializeAmount() {
        return Amount != null;
    }
    static void Main() {
        Data d = new Data();
        XmlSerializer ser = new XmlSerializer(d.GetType());
        ser.Serialize(Console.Out, d);
        Console.WriteLine();
        Console.WriteLine();
        d.Amount = 123.45M;
        ser.Serialize(Console.Out, d);
    }
}

More information on ShouldSerialize* on MSDN.

There is also an alternative to get

 <amount /> instead of <amount xsi:nil="true" />

Use

[XmlElement("amount", IsNullable = false)]
public string SerializableAmount
{
    get { return this.Amount == null ? "" : this.Amount.ToString(); }
    set { this.Amount = Convert.ToDouble(value); }
}