code: protected Set<String> normalizeWhitelist(Set<String> whitelist) {
      Set<String> result = new HashSet<>();
      for (String line : whitelist) {
        String trimmed = line.trim();
        if (trimmed.isEmpty() || trimmed.charAt(0) == '#') {
          // strip out empty lines and comments.
          continue;
        }
  
        // Strip line number for matching.
        result.add(LINE_NUMBER.matcher(trimmed).replaceFirst(":"));
      }
      return ImmutableSet.copyOf(result);
    }
docs: Loads legacy warnings list from the set of strings. During development line
  numbers are changed very often - we just cut them and compare without ones.
  
  @return known legacy warnings without line numbers.