新手请教：在新增窗体中出现“运行时错误"3421"，数据类型转换错误”提示，请帮忙解决，谢谢！

AccDev

基本状况：在表中单价字段设为货币，在新增窗体中单价字段设成自动填充，录入时出现如下问题：1、如果单价字段填充的是空格，就会出现“运行时错误"3421"，数据类型转换错误”提示（下面黄底代码就是按调试后指向需要调试的代码），2、如果是手动填入，单价字段数字前会有货币符号，自动填充的就没有，3、如将单价字段设成文本，就不会出现上述错误提示，4、在修改窗体中自动填充会出现货币符号，如果是空格也不会出现错误提示。

我是新手，无法解决，在此致以万分感谢，希望请大人们能帮忙解决，谢谢！

Private Sub cmd_Save()
Dim rst As DAO.Recordset
If IsNull(Me.fh) Then
MsgBox "请输入房号!", vbCritical, "提示："
Me.fh.SetFocus
Exit Sub
End If
If IsNull(Me.fwdz) Then
MsgBox "请输入房屋地址!", vbCritical, "提示："
Me.fwdz.SetFocus
Exit Sub
End If
If IsNull(Me.lbmc) Then
MsgBox "请输入户型!", vbCritical, "提示："
Me.lbmc.SetFocus
Exit Sub
End If
If IsNull(Me.cx) Then
MsgBox "请输入朝向!", vbCritical, "提示："
Me.cx.SetFocus
Exit Sub
End If
Me.Refresh
If MsgBox("您确认要保存吗?", vbOKCancel + vbInformation, "提示") = vbOK Then
Set rst = CurrentDb.OpenRecordset("tblCodefw", dbOpenDynaset)
rst.AddNew
rst("fwID") = acchelp_autoid("F", 3, "tblCodefw", "fwID")
rst("fh") = Me.fh
rst("fwdz") = Me.fwdz
rst("lbmc") = Me.lbmc
rst("cx") = Me.cx
rst("ddj") = Me.ddj
rst("sdj") = Me.sdj
rst("dsdj") = Me.dsdj
rst("ssdj") = Me.ssdj
rst("lbID") = Me.lbID
rst.Update
rst.Close
Set rst = Nothing
'刷新数据
If IsLoaded("usysfrmMain") Then
DoCmd.Echo False
Forms!usysfrmMain!frmChild.SourceObject = "frm_Codefw_child"
DoCmd.Echo True
End If
MsgBox "保存成功!", vbInformation, "提示"
Me.fh = Null
Me.fwdz = Null
Me.lbmc = Null
Me.cx = Null
Me.ddj = Null
Me.sdj = Null
Me.dsdj = Null
Me.ssdj = Null
Me.lbID = Null
End If
End Sub

Private Sub lbmc_AfterUpdate()
    Me.ddj = Me.lbmc.Column(1)
    Me.sdj = Me.lbmc.Column(2)
    Me.dsdj = Me.lbmc.Column(3)
    Me.ssdj = Me.lbmc.Column(4)
    Me.lbID = Me.lbmc.Column(5)
End Sub

Private Sub cmdCancel_Click()
DoCmd.Close acForm, Me.Name
End Sub

Private Sub cmdOK_Click()
cmd_Save
End Sub