Allow Blank Entries in Range Excel? - arrays

Question

Below is the code. What I'm confused about is how to get the BuyOne, BuyTwo, BuyThree, BuyFour array (arrBuyer) to allow blank entries. Right now if an entry is blank it'll say it's an invalid entry, whereas I just want it skipped over. In addition, if ALL entries are blank, I want it where the code just assumes the user wants to run every possible entry.
The user enters codes into four specific slots on the left of the page as seen in the image. Currently the code checks a list off to the right of the page to see if values match. How do I go about doing the above?
If Range("reqFrDt") = vbNullString Or IsDate(Range("reqFrDt")) = False Then
MsgBox "From date missing..."
Range("reqFrDt").Select
End
Else
sFrDt = Range("reqFrDt")
End If
If Range("reqToDt") = vbNullString Or IsDate(Range("reqToDt")) = False Then
MsgBox "To date missing or invalid.."
Range("reqToDt").Select
End
Else
sToDt = Range("reqToDt")
End If
lastRow = Range("O" & Rows.Count).End(xlUp).Row
Set rBuyerList = Range("O1:O" & lastRow)
arrBuyer = Array("BuyOne", "BuyTwo", "BuyThree", "BuyFour")
For i = 0 To UBound(arrBuyer)
With Application
chkFind = .IfError(.Match(Range(arrBuyer(i)), Range("O1:O50"), 0), 0)
End With
If Range(arrBuyer(i)) = vbNullString Or chkFind = False Then
MsgBox "Invalid Buyer Code.." & arrBuyer(i)
Range(arrBuyer(i)).Select
End If
Next i
Call runFinished(sFrDt, sToDt, arrBuyer)
Sheets("Main Sheet").Select
MsgBox ("done...")
End Sub
Sub runFinished(sFrDt As String, sToDt As String, arrBuyer As Variant)
Dim SQL As String
' add a new work sheet
ActiveWorkbook.Worksheets.Add
' dispay Criteria
Cells(1, 1) = "Run Date: " & Now()
Call MergeLeft("A1:B1")
Cells(2, 1) = "Criteria:"
Cells(2, 2) = "From " & Range("reqFrDT") & " -To- " & Range("reqToDt")
' SQL
SQL = "select a.StockCode [Finished Part], a.QtyToMake, FQOH,FQOO,/*FQIT,*/FQOA, b.Component [Base Material], CQOH,CQOO,CQIT,CQOA " & _
"from ( " & _
" SELECT StockCode, sum(QtyToMake) QtyToMake " & _
" from [MrpSugJobMaster] " & _
" WHERE 1 = 1 " & _
" AND JobStartDate >= '" & sFrDt & "' " & _
" AND JobStartDate <= '" & sToDt & "' " & _
" AND JobClassification = 'OUTS' " & _
" AND ReqPlnFlag <> 'I' AND Source <> 'E' Group BY StockCode " & _
" ) a " & _
"LEFT JOIN BomStructure b on a.StockCode = b.ParentPart " & _
"LEFT JOIN ( " & _
" select StockCode, sum(QtyOnHand) FQOH, Sum(QtyAllocated) FQOO, Sum(QtyInTransit) FQIT, Sum(QtyOnOrder) FQOA " & _
" from InvWarehouse " & _
" where Warehouse in ('01','DS','RM') " & _
" group by StockCode " & _
") c on a.StockCode = c.StockCode " & _
"LEFT JOIN ( " & _
" select StockCode, sum(QtyOnHand) CQOH, Sum(QtyAllocated) CQOO, Sum(QtyInTransit) CQIT, Sum(QtyOnOrder) CQOA " & _
" from InvWarehouse " & _
" where Warehouse in ('01','DS','RM') " & _
" group by StockCode " & _
") d on b.Component = d.StockCode "
SQL = SQL & _
"LEFT JOIN InvMaster e on a.StockCode = e.StockCode " & _
"WHERE 1 = 1 " & _
"and e.Buyer in ('" & Range(arrBuyer(0)) & "','" & Range(arrBuyer(1)) & "','" & Range(arrBuyer(2)) & "','" & Range(arrBuyer(3)) & "') " & _
"ORDER BY a.StockCode "