Search Items per vendor

I am working on the code that needs to search the items of a certain vendor. I think I have covered all the aspects I need to set the search criteria in my code (no compiling errors). But it did not return any item. Anybody dealt with SearchMultiSelectField object?

My code:

        Dim item_search As New ItemSearch
        Dim item_search_basic As New ItemSearchBasic

        Dim type() As String : ReDim type(10)
            type(0) = "_description"
            type(1) = "_discount"
            type(2) = "_inventoryItem"
            type(3) = "_itemGroup"
            type(4) = "_markup"
            type(5) = "_nonInventoryItem"
            type(6) = "_otherCharge"
            type(7) = "_payment"
            type(8) = "_service"
            type(9) = "_subtotal"

            Dim searchType As New SearchEnumMultiSelectField
            With searchType
                .operator = SearchMultiSelectFieldOperator.anyOf