private Set<String> findAllowedExtensions(java.nio.file.Path relativeDirectory) {
        Set<String> validExtensions = new HashSet<>();
        validExtensions.add(".gitignore");

        // Special case, since subdirs in schemas/ can have any name
        if (isSchemasSubDir(relativeDirectory))
            validExtensions.add(RANKPROFILE_NAME_SUFFIX);
        else
            validExtensions.addAll(validFileExtensions.entrySet().stream()
                                                      .filter(entry -> entry.getKey()
                                                                            .equals(Path.fromString(relativeDirectory.toString())))
                                                      .map(Map.Entry::getValue)
                                                      .findFirst()
                                                      .orElse(Set.of()));
        return validExtensions;
    }
Builder for {@link com.yahoo.config.model.application.provider.FilesApplicationPackage}. Use
this to create instances in a flexible manner.
config-application-package/src/main/java/com/yahoo/config/model/application/provider/FilesApplicationPackage.java