Add "go to next" if error encountered

Hi, I have the following code that colors a cell different colors based on the date compared to today in Column F. (red if it is in the past, yellow if it is today, etc.)

Recently had an issue with blanks and the value "NULL" in that field that cause the macro to crash. Need to modify this so that if it detects an error condition, it just goes to the next row instead of crashing.

Thanks in advance,

swjtx99

Dim C As Variant
Dim CI As Integer
Dim Col As Variant
Dim FirstRow As Long
Dim LastRow As Long
Dim rng As Range
Dim Wks As Worksheet
Dim monOffset As Integer
Dim targetDate As Date

    Col = "F"
    FirstRow = 2   'Assumes header row is row 1
    Set Wks = Worksheets("TEST1")
    LastRow = Wks.Cells(Rows.Count, Col).End(xlUp).Row
    LastRow = IIf(LastRow < FirstRow, FirstRow, LastRow)
   
    Set rng = Wks.Range(Cells(FirstRow, Col), Cells(LastRow, Col))
        targetDate = Now()
    For Each C In rng
        monOffset = 0
       
        Select Case Int(targetDate) - C
        Case Is > 0
            CI = 3   'Red
        Case Is = 0
            CI = 6   'Yellow
        Case Is < 0
            Select Case Weekday(C)
            Case 2  'Monday
                Select Case Int(targetDate) - C
                Case -3
                    CI = 4  'Green
                Case -4
                    CI = 35 'Pale Green
                Case Else
                    CI = xlColorIndexNone
                End Select
            Case 3  'Tuesday
                Select Case Int(targetDate) - C
                Case -1
                    CI = 4  'Green
                Case -4
                    CI = 35 'Pale Green
                Case Else
                    CI = xlColorIndexNone
                End Select
            Case Else
                Select Case Int(targetDate) - C
                Case -1
                    CI = 4  'Green
                Case -2
                    CI = 35 'Pale Green
                Case Else
                    CI = xlColorIndexNone
                End Select
            End Select
        End Select
       
        C.Interior.ColorIndex = CI
    Next