assertEquals("foo", sb.toString());  sb.append((StrBuilder) null);
    public void testAppend_StrBuilder() {        StrBuilder sb = new StrBuilder();        sb.append(new StrBuilder("foo"));        assertEquals("foo", sb.toString());        sb.append((StrBuilder) null);        assertEquals("foo", sb.toString());        sb.append(new StrBuilder(""));        assertEquals("foo", sb.toString());        sb.append(new StrBuilder("bar"));        assertEquals("foobar", sb.toString());    }