@Override
    public T addChar(K name, char value) {
        throw new UnsupportedOperationException("read only");
    }
@Test
    public void testAddChar() {
        assertThrows(UnsupportedOperationException.class, new Executable() {
            @Override
            public void execute() {
                HEADERS.addChar("name", 'a');
            }
        });
    }