关于variant变量的问题。

dim i as variant

我假设i可能是个空值（null）可能是个字符串。现在我有一个问题是，可以不通过判断把i传给一个函数，在里面去执行存储过程。见代码，
Public Function GetTaskInfo(ByVal condition_1 As Variant, _
ByVal condition_2 As Variant, _
ByVal condition_3 As Variant, _
ByVal condition_4 As Variant) As Recordset
Dim ado As AdoAccess
Dim Result As Boolean
Dim SQL As String
Dim Rec As ADODB.Recordset
Dim source As String

Set ado = New AdoAccess
Set GetTaskInfo = Nothing

Result = ado.OpenConnection(GetSetting("CMQC", "DataBase", "ConnectString"))
If Result = True Then
SQL = "exec GetTaskInfoByMultiCondition" + Chr(34) + condition_1 + Chr(34) + condition_2 + condition_3 + condition_4
Result = ado.GetRecordset(SQL, Rec)
If Result = True Then
Set GetTaskInfo = Rec
End If

Set Rec = Nothing
ado.CloseConnection
End If
Set ado = Nothing
End Function

我的condition_1,2,3,4可能是null，可能是字符串。望高手指点。谢谢了