Deserialize XML with optional tags

I have an XML with an optional tag as follows:

<Config>
    <MyTag>true<MyTag>
    <!-- more tags -->
</Config>

And the class-definition:

public class config {
    [System.Xml.Serialization.XmlElement("CheckForCompleteTransform")]
    public bool? CheckForCompleteTransform { get; set; }
}

This works if I either set the tag to what I provided within my example-XML above or I omit it completely. But what if I provide the tag as <MyTag/>? If this notation is used I want the serializer to set the corresponding property within my class to true, but I awlays get a

System.FormatException: the string literal '' is not valod for type Boolean

Any ideas on how to achieve this?