DataTables

I am trying to create a column that can display a dynamic number of values separated by a comma. This is a a controlled field that allows between 0 and 3 entries. For example, my JSON data looks like this (sanitized by hand, so apologies if I get a bracket wrong or something):

{"aaData":[{"info":{"client_id": 1, "client_name":"Sample Client Name"},"support":{"SupportType1":{"44":"SampleUser1", "56":"SampleUser2"}}}]}

What I want is to display "SampleUser1, SampleUser2".

Here is what I have tried with no luck

Attempt 1:
"aoColumns": [
{ "mDataProp": "info.client_name", "sWidth": "18%"},
{
"fnRender": function( o, val) {
return(val.join(", "))
}
},
{ "mDataProp": function() {return support.CSM.join()}}
]

Attempt 2:
"aoColumns": [
{ "mDataProp": "info.client_name", "sWidth": "18%"},
{ "mDataProp": function() {return support.CSM.join()}}
]

Attempt 3:
"aoColumnDefs": [
{
"fnRender": function ( o, val ) {
return val.join
},
"aTargets": [ 1 ]
}
],

Any ideas (I have been able to $.map over the data, assign it to a value, and then display it in the console, but when I try to return the value the table stops rendering.)