未将对象引用设置到对象的实例 vb。net

 Public Sub depart_spc(ByRef rs As Data.DataTable, ByVal a As String)
        Dim j As Integer
        Dim n As Integer
        Dim i As Integer
        ' n = 500
        Dim dt As DataTable = rs
        Dim dr As DataRow = dt.NewRow()   ‘  出现未将对象引用设置到对象的实例 怎么解决啊
        Do
            a = Trim(a)
            j = InStr(1, a, " ")
            ' For i = 0 To 500
            If j <> 0 Then
                dr(0) = a.Substring(0, j - 1)
                a = Mid(a, j + 1)
            ElseIf Len(a) <> 0 Then
                dr(0) = a
                a = ""
            End If
            ' Next
        Loop Until Len(a) = 0
        dt.Rows.Add(dr)

    End Sub

你上层调用送进来的 rs 本身就是 Nothing。

rs是不是不是DataTable对象转类型失败或者本身为NULL