As found by errorprone:
jaxp/src/java.xml/share/classes/com/sun/org/apache/xalan/internal/xsltc/compiler/AttributeSet.java

    public void parseContents(Parser parser) {

        // Get this attribute set's name
        final String name = getAttribute("name");

        if (!XML11Char.isXML11ValidQName(name)) {
            ErrorMsg err = new ErrorMsg(ErrorMsg.INVALID_QNAME_ERR, name, this);
            parser.reportError(Constants.ERROR, err);
        }
        _name = parser.getQNameIgnoreDefaultNs(name);
        if ((_name == null) || (_name.equals(EMPTYSTRING))) {

_name is a QName, while name is a String. The author probably confused these two. (_name.equals(EMPTYSTRING)) is always false.