In XML there are two conventions for storing a value:
If you set the message set property Encoding Null Num to NULLElement, there is no way to represent a null value for an attribute value. If a null value is present in the tree (from ESQL or another format), an attribute with an empty string is written in the output message.
Conversely, if you have set the message set property Encoding Null Num or Encoding Null Non-Num to NULLValAttr, there is no way to represent a null value for a value rendered as XML content. If a null value is present in the tree, when writing an empty string, an element with no character content is written out instead.