Vb.net 将datagridview数据传递给另一个datagridview'；System.NullReferenceException'；

我需要帮助解决这个问题，但我不知道如何解决这个问题

这就是代码

Private Sub GetLabandOtherFees()
        Dim dic As New Dictionary(Of String, Integer)()
        Dim cellValue As String = Nothing
        For i As Integer = 0 To dgvSubjectsEnrolled.Rows.Count - 1
            If Not dgvSubjectsEnrolled.Rows(i).IsNewRow Then
                cellValue = dgvSubjectsEnrolled(0, i).Value.ToString()
                If Not dic.ContainsKey(cellValue) Then
                    dic.Add(cellValue, 1)
                Else
                    dic(cellValue) += 1
                End If
            End If
        Next

        Dim sb As New StringBuilder()
        For Each keyvalue As KeyValuePair(Of String, Integer) In dic
            sb.AppendLine(String.Format("{0}", keyvalue.Key, keyvalue.Value))
        Next

        For Each row As DataGridViewRow In dgvsub.Rows
            row.Cells(0).Value = sb.ToString()
            row.Cells(1).Value = dic.Count.ToString()
        Next
    End Sub

这就是错误

"Object Reference Not set to an instance of an object." 
Check to determine if object is null before calling the method.

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这个错误使我头痛。请帮助。

阅读错误内容。在这里，试试这个，只需在其中添加一点条件

               If dgvSubjectsEnrolled(0, i).Value > 0 Then
                    cellValue = dgvSubjectsEnrolled(0, i).Value.ToString()
                    If Not dic.ContainsKey(cellValue) Then
                        dic.Add(cellValue, 1)
                    Else
                        dic(cellValue) += 1
                    End If
                Else
                End If

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在这段代码中，错误发生在什么地方？错误看起来是什么样子？这部分。“cellValue=dgvSubjectsEnrolled（0，i）.Value.ToString（）”是的！谢谢。干得好。。