Parsing JsonData throws error when value is null, what to do?

Using LitJson and the Facebook graph api inside a Unity webplayer build is giving me problems with data parsing.

Data:

 {"data":[{"name":"Red Green","uid":111111111,"wall_count":null,"pic":"http:\/\/profile.ak.fbcdn.net\/hprofile-ak-snc4\/11111_111111111_2289168_s.jpg"}]}

Offender:

 JsonData myListing = _return;  //the Json data above
 for(int i = 0; i<myListing["data"].Count; i++)
 {
     holdText += i.ToString() + ": " + myListing["data"][i]["name"] + "          ";
     holdText += myListing["data"][i]["wall_count"].ToString() + "              ";
     holdText += myListing["data"][i]["pic"] + "\n";
 }

Any line of code that references ["wall_count"] will result in an error if the value is null. The problem is compounded because the code runs in the web player plug-in that does not provide error information.

So, if I can expect "wall_count" values to be null, how can I check without throwing the error?

myListing["data"][i].Count is 4, so there are 4 objects there (name,uid,wall_count,pic), but trying to access the wall_count one will fail.