getDate()function

Any value that we want to parse as a valid date (defaults to undefined).
- Date instance returns unchanged (BUT if the date isn't valid, undefined is returned).
- null or undefined or "" empty string returns undefined
- The string "now" returns the current date (e.g. new Date()).
- The string "today" returns the current date at midnight (e.g. getMidnight()).
- The string "tomorrow" returns tomorrow's date at midnight (e.g. addDays(getMidnight(), 1)).
- The string "yesterday" returns yesterday's date at midnight (e.g. addDays(getMidnight(), 1)).
- Date strings (e.g. "2003-09-12" or "2003 feb 20:09") return the corresponding date (using the user's current locale).
- Time strings (e.g. "18:32" or "23:59:59.999") return today's date at that time (using the user's current locale).
- Numbers are return the corresponding date (using new Date(number), i.e. milliseconds since 01/01/1970).
- Anything else returns undefined required

Date instance if the value could be converted to a valid date, or undefined if not.