getDate
Gets a property's value as an Instant date. JSON does not directly support dates, so the actual property value must be a string, which is then parsed according to the ISO-8601 date format (the default used in JSON.) Returns null if the value doesn't exist, is not a string, or is not parsable as a date. NOTE: This is not a generic date parser! It only recognizes the ISO-8601 format, with or without milliseconds.
Return
the Instant date value or null.
Parameters
key
the key