没有为 类型“Hashtable” 和 'Nothing' 定义运算符“=”??

[hdf336]

用hashtable做的购物车:
添加商品:
Protected Sub dgview_ItemCommand(ByVal source As Object, ByVal e As System.Web.UI.WebControls.DataGridCommandEventArgs) Handles dgview.ItemCommand
If e.CommandName = "addshop" Then
Dim petid As String = dgview.DataKeys(e.Item.ItemIndex).ToString
If Session("bus") = Nothing Then '在这个地方出现错误没有为 类型“Hashtable” 和 'Nothing' 定义运算符“=”??
Dim ht As System.Collections.Hashtable = New Hashtable()
ht.Add(petid, 1)
Session("bus") = ht
Else
Dim ht As System.Collections.Hashtable = CType(Session("bus"), Hashtable)
If ht(petid) = Nothing Then
ht(petid) = 1
Else
ht(petid) = Convert.ToInt32(ht(petid)) + 1
End If
Session("bus") = ht
End If

Response.Write("<script>alert('商品添加成功！');</" & "script>")
End If
End Sub

[Red_angelX]

is Nothing

[blueskygenius]

is Nothing