YAJINTO with null

I am returning a json object that sometimes has a field that contains
"null", tax in the example below: How can I code my program to handle this
field when it is null? I am loading up result using data-into

processed_at "2019-01-29T13:47:58+00:00"
po_number "P347235"
invoice_number "400623985"
totals
net "462.31"
tax null
total "462.31"
carriage null
Dcl-ds result qualified dim(100);
processed_at char(10);
po_number char(7);
invoice_number char(10);
Dcl-ds totals;
tax char(10);
End-ds;