Specification for javax.xml.stream.XMLStreamReader.getProperty() states:

"
getProperty

Object getProperty(String name)
                   throws IllegalArgumentException

    Get the value of a feature/property from the underlying implementation

    Parameters:
        name - The name of the property, may not be null
    Returns:
        The value of the property
    Throws:
        IllegalArgumentException - if name is null
"

but it does not describe method behavior in case if there is no property with name "name". Please note that there is no list of mandatory supported properties as well.