Error while setting triangles list of submesh from C#

I'm trying to refactor my code that was using a single mesh, splitting it into submeshes.

I'm using SetTriangles method of Mesh object, like suggested in my previous question.

In the previous and working version I had the following lines:

 List<int> triangles = new List<int>();
 
 ...
 //fill up vertex buffer, triangles list and uv..
 mesh.triangles = triangles.ToArray();

Now I'm trying the following:

 List<int> triangles = new List<int>();
     
 ...
 //fill up vertex buffer, triangles list and uv..
 mesh.subMeshCount = 1;
 mesh.SetTriangles(triangles.ToArray(),0); //compiler error here

But I have a compiler error on the last line:

 error CS0029: Cannot implicitly convert type 'void' to 'int[]'

Now the return type of ToArray is actually int[]. So, I don't know how to fix this.

Could someone tell me what's the error here?