`InetAddressMatchers.matchExternal()` matches `null` and `0.0.0.0`

[philwebb]

Describe the bug

InetAddressMatchers.matchExternal().build() returns a negated matchInternal() builder, however, I'm not sure that null or 0.0.0.0 should be classified as external addresses.

To Reproduce

InetAddressMatcher matcher = InetAddressMatchers.matchExternal().build();
assertThat(matcher.matches(null)).isFalse();
assertThat(matcher.matches("0.0.0.0")).isFalse();
assertThat(matcher.matches("::")).isFalse();

Expected behavior
See above

Sample
See above