How to check for a value OR NULL on custom enddate field using yii syntax when calling entries?
Shooting in the dark here, but looking off this ticket and the ECM parameter value syntax in the docs, could you do something like:

{% paginate craft.entries({
    section : 'dealDirectory',
    limit   : pageSize,
    startDate : '&lt;=' ~ now
    endDate: 'or', '&gt;= ' ~ now, 'not null'
}) as pageInfo, dealEntries %}


The or is a total guess based on the and in the other ticket.