While working JENKINS-42120 some bugs in the JDL Dropdown became evident:

1. Adjust the height of dropdown to match that of standard button.
2. Prevent NPE if "data" prop is null/undefined
3. Need better UX if the "data" prop is an empty array. Right now an empty menu opens which looks odd. Should either prevent the menu from displaying, or perhaps display it with some kind of "no options" menu.