Using Dictionary.Exists in a UserForm property is giving Error 404 object required

Question

I am trying to use Class properties Get and Let in a UserForm called UBidStatus to fill a dictionary called DicOption.
Everything works fine until the If Not DicOption(OptName).Exists line (Error 404 object required).
NOTE: The code is working if I replace the whole code in the Public Property Let by DicOption.Add key:=OptName, Item:=OptValue.
This is the code in the Userform Class that I am trying to fix.

'Userform Class Module
Private DicOption As scripting.Dictionary

Public Property Get ProjectOption(ByVal OptName As String) As String
    ProjectOption = UBidStatus.ProjectOption(OptName)
End Property

Public Property Let ProjectOption(ByVal OptName As String, ByVal OptValue As String)
    If Not DicOption(OptName).Exists Then
        DicOption.Add key:=OptName, Item:=OptValue
    Else
        DicOption(OptName) = OptValue
    End If
End Property

Public Sub UserForm_Initialize()
    Set DicOption = New scripting.Dictionary
End Sub

Private Sub UserForm_Terminate()
    Set DicOption = Nothing
End Sub

Public Sub ExchangeToDicOption()
    Dim LR As Long
    Dim Rg As Range
    Dim ws As Worksheet
    Dim i As Long
    Dim a As String
    Dim b As String

    Set ws = ActiveWorkbook.Worksheets(2)
    Set Rg = ws.Columns(2)

    DicOption.RemoveAll

    LR = Rg.Find(What:="*", Lookat:=xlPart, LookIn:=xlFormulas, SearchOrder:=xlByRows, _
        SearchDirection:=xlPrevious, MatchCase:=False).Row

    If LR > 1 Then
        For i = 2 To LR
            a = Cells(i, 1)
            b = Cells(i, 2)
           UBidStatus.ProjectOption(a) = b
        Next i
    End If
End Sub

Answer 1

The Exists method is called like this:

Dictionary.Exists(Key)

So try

 Public Property Let ProjectOption(ByVal OptName As String, ByVal OptValue As String)
    If Not DicOption.Exists(OptName) Then
        DicOption.Add key:=OptName, Item:=OptValue
    Else
        DicOption(OptName) = OptValue
    End If
End Property

Answer 2

A Scripting.Dictionary will implicitly call its Add method if you assign to a key that doesn't exist, so if the goal is to "add or replace" the value at the specified key, you could simply replace:

If Not DicOption(OptName).Exists Then
    DicOption.Add key:=OptName, Item:=OptValue
Else
    DicOption(OptName) = OptValue
End If

with:

DicOption.Item(OptName) = OptValue