@SuppressWarnings("unchecked")
    public <T> Schema<T> getTargetSchema()
    {
        return (Schema<T>) targetSchema;
    }
Thrown when attempting to build a protocol message that is missing required fields. This is a
{@code RuntimeException} because it normally represents a programming error: it happens when some code which
constructs a message fails to set all the fields.

@author kenton@google.com Kenton Varda
@author David Yu
protostuff-api/src/main/java/io/protostuff/UninitializedMessageException.java