public void validate() {
        if (this.monthMap == null || this.monthMap.isEmpty()) {
            throw new IllegalStateException("Month Map is required.");
        }
        if (this.inputTimeZone == null) {
            throw new IllegalStateException("Input TimeZone must be non-null.");
        }
        if (this.outputTimeZone == null) {
            throw new IllegalStateException("Output TimeZone must be non-null.");
        }
    }