@ctweney  nil/blank related check:

irb(main):001:0> DateTime.parse("")
ArgumentError: invalid date
	from /Users/yuhung/.rvm/rubies/jruby-1.7.2/lib/ruby/1.9/date.rb:1691:in `new_by_frags'
	from /Users/yuhung/.rvm/rubies/jruby-1.7.2/lib/ruby/1.9/date.rb:1736:in `parse'