NullReferenceException was unhandled - C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MathNet.Numerics.LinearAlgebra;
using MathNet.Numerics.LinearAlgebra.Double;
 
namespace MultiplyMatrixNumerics
{
    class Program
    {
        /*  static void mult(Matrix<double> A, Matrix<double> B, ref Matrix<double> C)
          {
              C = A.ConjugateTransposeAndMultiply(B);
          
          }
         * */
        static int Clas = 6;
 
        static void Main(string[] args)
        {
            Matrix<double> AParcel = DenseMatrix.OfArray(new double[,] {
                {1,1,1,1},
                {1,2,3,4},
                {4,3,2,1}});
            Matrix<double> B = DenseMatrix.OfArray(new double[,] {
                {1,2,3,4},
                {5,6,7,8},
                {4,3,2,1}});
            Matrix<double> B_Tr = B.Transpose();
            Matrix<double> AB1 = AParcel.Multiply(B_Tr);
            //Console.WriteLine(C.ToString());
 
            // A = B.SubMatrix(1, 2, 0, 2);
            //Console.WriteLine(A.ToString());
            Matrix<double> AParcel2 = DenseMatrix.OfArray(new double[AParcel.RowCount, AParcel.ColumnCount]);
            for (int i = 0; i < AParcel.RowCount; i++)
            {
                for (int j = 0; j < AParcel.ColumnCount; j++)
                {
                    AParcel2[i, j] = AParcel[i, j] * AParcel[i, j];
                }
            }
 
            Matrix<double> B_Tr2 = DenseMatrix.OfArray(new double[B_Tr.RowCount, B_Tr.ColumnCount]);
            for (int i = 0; i < B_Tr.RowCount; i++)
            {
                for (int j = 0; j < B_Tr.ColumnCount; j++)
                {
                    B_Tr2[i, j] = B_Tr[i, j] * B_Tr[i, j];
                }
            }
 
            // Console.WriteLine(AParcel2);
            Vector<double> aParcel = AParcel2.RowSums();
            Vector<double> bParcel = B_Tr2.ColumnSums();
            // aParcel.ToRowMatrix();
            // bParcel.ToColumnMatrix();

            Matrix<double> RR1 = DenseMatrix.OfArray(new double[AB1.RowCount, AB1.ColumnCount]);
            for (int i = 0; i < AParcel.RowCount; i++)
            {
                for (int j = 0; j < B_Tr.ColumnCount; j++)
                {
                    RR1[i, j] = aParcel[i] + bParcel[j] - 2 * AB1[i, j];
                    // AB1.MapIndexedInplace((i, j, x) => aParcel[i] + bParcel[j] - 2 * x);
 
                }
            }
            //Console.WriteLine(RR1);
            //var MinElRow = Vector<double>.Build.DenseOfEnumerable(matrix.EnumerateRows().Select(x => x.Min()));
            //var MinElCol = Vector<double>.Build.DenseOfEnumerable(matrix.EnumerateColumns().Select(x => x.Min()));
            Vector<double> MinRR1Row = Vector<double>.Build.DenseOfEnumerable(RR1.EnumerateRows().Select(x => x.Min()));
            Vector<double> MinRR1Column = Vector<double>.Build.DenseOfEnumerable(RR1.EnumerateColumns().Select(x => x.Min()));
            Matrix<double> MinRR1RowM = MinRR1Row.ToRowMatrix();
            Matrix<double> MinRR1ColumnM = MinRR1Column.ToColumnMatrix();
            Vector<double> MinRR1RowM_Summ = MinRR1RowM.RowSums();
            Vector<double> MinRR1ColumnM_Summ = MinRR1ColumnM.ColumnSums();

            Vector<double> V = MinRR1RowM_Summ / AB1.ColumnCount;
            Vector<double> V1 = MinRR1ColumnM_Summ / AB1.RowCount;

            //Console.WriteLine(MinRR1ColumnM);
            // Console.WriteLine(MinRR1RowM);
            // Console.WriteLine(MinRR1RowM_Summ);
            // Console.WriteLine(MinRR1ColumnM_Summ);
            Console.WriteLine(V);
            Console.WriteLine(V1);
            /*
                for (int j = 0; j < AB1.ColumnCount; j++)
                {
                    for (int i = 0; i < AB1.RowCount; i++)
                    {
                        
                    }
                }

                for (int i = 0; i < AB1.ColumnCount; i++)
                {
                    for (int j = 0; j < AB1.RowCount; j++)
                    {
 
                    }
                }
                    
            */
 
            //Console.WriteLine(RR1);
            //Console.WriteLine();
 
            // Matrix<double> cRowSums_Matrix = C.RowSums();
            //Matrix<double> cColumnSums_Matrix = C.ColumnSums();
            Vector<double> VV = null;
            Vector<double> VV1 = null;
            Vector<double> probability = DenseVector.OfArray(new double[] {2.1, 4.2, 4.3, 5.1, 7.8});
            VV = V; 
            VV1 = V1;
 
            double PMAX = -1;
            double PMAX1 = -1;
            int JMAX = 1;
            int JMAX1 = 1;
            kol.ProbabilityMax(Clas, VV, VV1, out probability,  PMAX,  PMAX1,  JMAX,  JMAX1);
            Console.WriteLine(probability);
            Console.WriteLine("P",PMAX);
            Console.WriteLine("P1",PMAX1);
            Console.WriteLine("J",JMAX);
            Console.WriteLine("J1",JMAX);
            string h;
            h = Console.ReadLine();
        }
    }
 
    class kol
    {
 
        public static void ProbabilityMax(int Clas, Vector<double> VV, Vector<double> VV1, out Vector<double> probability,  double PMAX,  double PMAX1, int JMAX, int JMAX1)
        {
           
            probability = null;
            Vector<double> SumPrJ = null;
            Vector<double> pr = DenseVector.OfArray(new double[1]);//Clas
            for (int i = 0; i < 1; i++)//1 - Clas - 1
            {
                pr[i] = (VV1[i]) + (VV[i]);
 
            }
            pr.MapInplace(x => 1 / x);
            for (int j = 0; j <1; j++)//Clas - 1
            {
                SumPrJ += pr[j];
            }
 
            for (int i = 0; i < 1; i++)//Clas - 1
            {
                probability = (pr[i]) / (SumPrJ);
 
            }
 
            for (int jj = 0; jj < 1; jj++)//Clas - 1
            {
                if (probability[jj] > PMAX)
                {
                    JMAX = jj;
                    PMAX = probability[jj];
 
                }
            
            }
 
            probability[JMAX] = -1.0;
 
            for (int jj = 0; jj < 1; jj++) //Clas - 1
            {
                if (probability[jj] > PMAX1)
                {
                    JMAX1 = jj;
                    PMAX1 = probability[jj];
 
                }
                
            }
            probability[JMAX] = PMAX;
        }
    }
}

 for (int j = 0; j <1; j++)//Clas - 1
            {
                SumPrJ += pr[j];
            }