title: How does one create optional command line arguments in oozie workflow xml
body: <p>Please bear in mind that I'm a complete rookie with oozie. I know that one can specify command line arguments in the oozie workflow xml by using the arg tag. I wondered how it is possible to specify an optional command line argument such that oozie will not complain that a required parameter is missing if the user doesn't specify it?</p>
  
  <p>Many thanks in advance. If the information I've given is not specific enough, I can provide a concrete example when I log into my work machine tomorrow. We use apache commons CLI options to parse the options.</p>
  
  <p>E.g. I want to make the following argument optional:</p>
  
  <p>-e${endDateTime}</p>