why my transaction cost is null, while actual_cost, prior_cost, and new_cost have value?

Dear All,

I am confuse  with how oracle calculate the costs. I transaction cost is null while actual cost, prior cost and new cost have value.

why this is happening? I mean why can the transaction cost is null but actual cost, prior cost and new cost have value, isn't it just copy and past from new cost?

please help me to resolve this issue.

Thanks in advance.

Best Regards,

Dian