CollectionMagic.cs

var result = obj.createResult(resultType);
result.add(new LineItem("A"));
result.add(new LineItem("B"));
Utility.populate(dependency, obj, "C", "D", "E");
result.add(new LineItem("F");
return result;

CollectionMagicTry1.cs

var result = obj.createResult(resultType,
   new LineItem("A"),
   new LineItem("B"));
Utility.populate(dependency, obj, "C", "D", "E");
result.add(new LineItem("F"));
return result;

// populate returns void
// createResult(ResultType, params LineItem[] lineItems)

CollectionMapTry2.cs

var result = obj.createResult(resultType, new List<LineItem>
{
   new LineItem("A"),
   new LineItem("B"))
}.Union(CThoughE(dependency,
   "C",
   "D",
   "E")
).Union(new List<ListItem>
{
   new LineItem("F")
};

return result;


// CThoughE is a new method I created that returns IEnumerable (the utility function returned void)
// createResult(ResultType, IEnumerable<LineItem>)