Data Tables sorting not working for some columns in table (the value "NA" is creating the issue)

Hii,

In my table few columns have "NA" where there is no data. Only two columns throws wrong sorting with "NA" and other columns are working fine with "NA" data also considering "NA" as highest value. I tried to extend logic by replacing "NA" with "-1" and doing custom sorting for that column but nothing works. Please any one help me to solve this issue.

Thanks,
Sri.