[Tracker] Help: Can I remove data by condition "some field is empty"?

["Zhang, Jingke" <jingke zhang intel com>]

Hi all,
    I am new here in tracker-list. When I search contact data, I found some data with blank "nco:fullname". 
Then I try to remove them, but failed. 
    My tracker is 0.9.16. Can tracker support "remove data by blank value condition"? Thanks!

    Detail steps:
    ==========
    # tracker-sparql -q "SELECT nco:fullname(?a) nco:nickname(?a) WHERE { ?a a nco:PersonContact }"
    Results: 3
     ， 
     ，
     ，
    # tracker-sparql -u --query="DELETE { ?a a nco:PersonContact } WHERE { ?a nco:fullname '' } "
    No effect...