Path orRethrow() {
            if (this.path == null) {
                throw this.exception;
            }
            return this.path;
        }
Contains a Path, or an Exception in case the Path is invalid.

<p>It is used for Java system properties "user.home" and "user.dir" to delay throwing the Exception.

<p>Even if "user.home" or "user.dir" is invalid, it should be okay when "embulk_home" is configured explicitly.
embulk-core/src/main/java/org/embulk/cli/EmbulkSystemPropertiesBuilder.java