code: static void ensureHostnamePatternMatchesDefaultHostname(String hostnamePattern, String defaultHostname) {
          if ("*".equals(hostnamePattern)) {
              return;
          }
  
          // Pretty convoluted way to validate but it's done only once and
          // we don't need to duplicate the pattern matching logic.
          final DomainNameMapping<Boolean> mapping =
                  new DomainNameMappingBuilder<>(Boolean.FALSE).add(hostnamePattern, Boolean.TRUE).build();
  
          if (!mapping.map(defaultHostname)) {
              throw new IllegalArgumentException(
                      "defaultHostname: " + defaultHostname +
                      " (must be matched by hostnamePattern: " + hostnamePattern + ')');
          }
      }
docs: Ensure that 'hostnamePattern' matches 'defaultHostname'.