Clone and CopyTo method of GXDLMSObject class does not work C#

GXDLMSObject writeData = item.GXDLMSObject;
GXDLMSObject readData;
if (writeData is not null)
{
readData = writeData.Clone();
}
When cloning to readData, the error "System.ArgumentNullException: "Value cannot be null. Arg_ParamName_Name", although writeData is not null.
The same situation when using the CopyTo() method;