How to stop JiBX from marshalling empty nodes for null fields on structure mapping

Use a test-method on the structure to return false if the field value is null.
Note: This can be applied only when the usage attribute is set to optional (ie. usage="optional")

E.g.

<structure name="CreditCard" field="creditCard"  usage="optional" test-method="hasValidCredtiCard">
    <value name="CardNumber" field="number" usage="optional"/>
    <value name="ValidThru" get-method="getValidThru" set-method="setValidThru" usage="optional"/>
    <value name="NameOnCard" field="name" usage="optional"/>
    ....
</structure>