In the method 'sun.nio.cs.CharsetMapping#readINDEXC2B'

    void readINDEXC2B() {
        char[] map = readCharArray();
        for (int i = map.length - 1; i >= 0; i--) {
            if (c2b == null && map[i] != -1) {
                c2b = new char[map[i] + 256];
                Arrays.fill(c2b, (char)UNMAPPABLE_ENCODING);
                break;
            }
        }
        c2bIndex = map;
    }

Condition 'map[i] != -1' is always true. 'char' values range [0..65535]. It can't be equal to '-1'