Error in call to VolunteerNeed_get : start_time is not a valid date:

Steps to reproduce:

• pull up civicrm/a/#/volunteer/opportunities in your browser
• supply "between X and Y" dates and click search
• wait for your search results
• click the X next to each date to repeat the search with no date criteria
• click search
• the message "Error in call to VolunteerNeed_get : start_time is not a valid date:" appears
• click search again
• wait for your search results