Render function not being called

I cannot get the render function to be called on my datatable. The data source is an AJAX call and the data comes in fine. But I want to add a link to one of the fields so I am using a render function on that column to build the link.

Here is the pertinent code:

"ajax":{
          "url":"ajaxtest.cfc?method=getData",
          "dataSrc": "DATA",
          "columns": [
              {"DATA":"ROLLYEAR"},
              {"DATA":"APN",
                "render": function (data){
                  if (data !== null){
                   return "<a href='pagelink.cfm?id="+data+"'>"+apn+"</a>";
                } else {
                  return "<a href='pagelink.cfm?id="+data+"'>"+apn+"</a>";
                }
                }},
              {"DATA":"ARCNUMBER", "render":"test"},
              {"DATA":"APPRAISER"},
              {"DATA":"ARCGENERATEDDATE"},
              {"DATA":"STATUS"},
              {"DATA":"APPROVEDBY"},
              {"DATA":"CALAMITYTYPE"},
              {"DATA":"DIST"},
              {"DATA":"NGH"},
              {"DATA":"CL"}
            ]
          }

No matter what I try the APN column is always generated as is with no link. I've even tried putting a console.log in the render function and get no output to the console. I've tried making the render function something simple like outputting a different text string and still it doesn't work. The data being returned looks like this:

{"COLUMNS":["ROLLYEAR","APN","ARCNUMBER","APPRAISER","ARCGENERATEDDATE","STATUS","APPROVEDBY","CALAMITYTYPE","DIST","NGH","CL","ID","ARCID"],"DATA":[[####,"XXXXX",####,###,"XXXX-XX-XX","XXXX","XXXXX","XXXXX",###.#,###,null,####,####]]}

(I've replaced the data with ### for numbers and XXXX for text fields as the data is a bit sensitive.)

I've tried the more complete render function that looks like this: "render":function (data, type, row,meta) but that doesn't make any difference either.

Any ideas? I'm at my wits end. I have read many queries on similar issues and I can't get any of those solutions to work here though it looks like it should. I'm sure I'm missing something obvious.

Thanks for any help.