The use case:
    A SAX parser is created;
    A Catalog is set on the parser;
    The XML to be parsed contains XInclude file;
    Since we're using the Catalog, the parsing was started without a handler (handler = null).

The result was the file was not parsed successfully, instead an Exception was thrown:
org.xml.sax.SAXParseException; lineNumber: 3; columnNumber: 25; An include with href 'test.xml'failed, and no fallback element was found.