api/tes: ListTasks tag filter fix for empty string as value of tag in dynamodb
api/tes: ListTasks tag filter fix for empty string as value of tag in dynamodb

ohsu-comp-bio/funnel,adamstruck/funnel,ohsu-comp-bio/funnel,adamstruck/funnel,ohsu-comp-bio/funnel,ohsu-comp-bio/funnel,adamstruck/funnel,adamstruck/funnel