The graphToRdf function in RDFDataset.java checks whether any of the keys in the JSON document are reserved JSON-LD keywords. As JsonLdUtils.isKeyword() doesn't know of @version (introduced in 1.1), it then tries to interpret its value, which fails.

Solution: add || "@version".equals(key) to the isKeyword function in JsonLdUtils.java:

    /**
     * Returns whether or not the given value is a keyword (or a keyword alias).
     *
     * @param v
     *            the value to check.
     * @param [ctx]
     *            the active context to check against.
     *
     * @return true if the value is a keyword, false if not.
     */
    static boolean isKeyword(Object key) {
        if (!isString(key)) {
            return false;
        }
        return "@base".equals(key) || "@context".equals(key) || "@container".equals(key)
                || "@default".equals(key) || "@embed".equals(key) || "@explicit".equals(key)
                || "@graph".equals(key) || "@id".equals(key) || "@index".equals(key)
                || "@language".equals(key) || "@list".equals(key) || "@omitDefault".equals(key)
                || "@reverse".equals(key) || "@preserve".equals(key) || "@set".equals(key)
                || "@type".equals(key) || "@value".equals(key) || "@vocab".equals(key)
                || "@requireAll".equals(key) || "@version".equals(key);
    }