@Test
    public void requireThatToHexStringAcceptsNull() {
        assertNull(HexDump.toHexString(null));
    }
@author Simon Thoresen Hult
@author <a href="mailto:steinar@yahoo-inc.com">Steinar Knutsen</a>
vespajlib/src/test/java/com/yahoo/io/HexDumpTestCase.java