public Path inputFile(String key, String description, Path defaultValue) {
    Path path = file(key, description, defaultValue);
    if (!Files.exists(path)) {
      throw new IllegalArgumentException(path + " does not exist");
    }
    return path;
  }
Returns a {@link Path} parsed from {@code key} argument which must exist for the program to function.

@throws IllegalArgumentException if the file does not exist
planetiler-core/src/main/java/com/onthegomap/planetiler/config/Arguments.java