C# Component Error. Help me

I want to make components with C # Express. What is the problem with my coding? An error occurs. Only "null" is output. I want to outputpolyline. Please correct my code

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using System;
using System.Collections.Generic;
using System.Text;
using Grasshopper.Kernel;
using Rhino.Geometry;

namespace ClassLibrary1
{
public class Fachwerk: GH_Component
{

public Fachwerk():
base("Fachwerk","Fachwerk","Fachwerkstaebe","JinsooKim","Stab"){}

protected override void RegisterInputParams(GH_Component.GH_InputParamManager pManager)
{
pManager.Register_PointParam("Point","P","Input Point");
pManager.Register_IntegerParam("DivU","U","U-Divide");
pManager.Register_IntegerParam("DivV","V","V-Divide");

}

protected override void RegisterOutputParams(GH_Component.GH_OutputParamManager pManager)
{
pManager.Register_CurveParam("Curve","A","Cirve list");
pManager.Register_CurveParam("Curve","B","Cirve list");
pManager.Register_CurveParam("Curve","C","Cirve list");
pManager.Register_CurveParam("Curve","D","Cirve list");

}

protected override void SolveInstance(IGH_DataAccess DA)
{

Point3d pts = new Point3d();
int divU = new int();
int divV = new int();

if (DA.GetData(0, ref pts)) {
if (DA.GetData(1, ref divU)) { return; }
if (DA.GetData(2, ref divV)) { return; }

List<Point3d> pts_list1 = new List<Point3d>();

pts_list1.Add(pts);
Point3d[,] ptsList = new Point3d[divU+1, divV+1];
int n = 0;

for (int i = 0; i <= divU; i++)
{
for (int j = 0; j <= divV; j++)
{
ptsList[i, j] = pts_list1[n];

n = n + 1;
}
}

List<Polyline> splLinesA = new List<Polyline>();

for (int i = 0; i <= divU - 4; i += 4)
{
for (int j = 0; j <= divV - 2; j += 2)
{
List<Point3d> ptArr = new List<Point3d>();

ptArr.Add(ptsList[i, j]);
ptArr.Add(ptsList[i + 2, j + 1]);
ptArr.Add(ptsList[i, j + 2]);
ptArr.Add(ptsList[i, j]);

Polyline pl = new Polyline(ptArr);

splLinesA.Add(pl);
}

}

DA.SetDataList(0, splLinesA);

List<Polyline> splLinesB = new List<Polyline>();
Polyline pl_B = new Polyline();
for (int i = 0; i <= divU - 4; i += 4)
{
for (int j = 0; j <= divV - 3; j += 2)
{
List<Point3d> ptArr = new List<Point3d>();

ptArr.Add(ptsList[i + 2, j + 1]);
ptArr.Add(ptsList[i + 4, j + 2]);
ptArr.Add(ptsList[i + 2, j + 3]);
ptArr.Add(ptsList[i + 2, j + 1]);

Polyline pl = new Polyline(ptArr);

splLinesB.Add(pl);
}

}
DA.SetDataList(1, splLinesB);

List<Polyline> splLinesC = new List<Polyline>();

for (int i = 0; i <= divU - 4; i += 4)
{
for (int j = 0; j <= divV - 3; j += 2)
{
List<Point3d> ptArr = new List<Point3d>();

ptArr.Add(ptsList[i, j + 2]);
ptArr.Add(ptsList[i + 2, j + 1]);
ptArr.Add(ptsList[i + 2, j + 3]);
ptArr.Add(ptsList[i, j + 2]);

Polyline pl = new Polyline(ptArr);

splLinesC.Add(pl);
}

}
DA.SetDataList(2, splLinesC);

List<Polyline> splLinesD = new List<Polyline>();

for (int i = 0; i <= divU - 4; i += 4)
{
for (int j = 0; j <= divV - 2; j += 2)
{
List<Point3d> ptArr = new List<Point3d>();

ptArr.Add(ptsList[i + 2, j + 1]);
ptArr.Add(ptsList[i + 4, j]);
ptArr.Add(ptsList[i + 4, j + 2]);
ptArr.Add(ptsList[i + 2, j + 1]);

Polyline pl = new Polyline(ptArr);

splLinesD.Add(pl);
}

}
DA.SetDataList(3, splLinesD);
}
}

public override Guid ComponentGuid
{
get {

return new Guid("{F85370B0-6C41-4579-AEEB-666A1E5BE175}");
}
}
}
}