Multiple Search Criteria To Bring Back Data

I have a dataset which is dumped into my model every month. The Report tab is a "user form" whereby the user can select multiple search criteria. The dataset is then filtered according to the search criteria entered by the user.

Problem is, that if the user only selects 1 of 3 search criteria and the other 2 cells are left blank, the filter filters on these blank cells and doesn't retrieve any data. Any ideas how I can overcome this?

Sub PopulateReport()

Application.ScreenUpdating = False

Dim MyFilter1 As String
Dim MyFilter2 As String
Dim MyFilter3 As String

MyFilter1 = CStr(Sheets("Report").Range("C2").Value) ' convert cell value to string
MyFilter2 = CStr(Sheets("Report").Range("C4").Value)
MyFilter3 = CStr(Sheets("Report").Range("C6").Value)

Sheets("Waste").Select

Dim Rw As Long
Dim Rng As Range

Rw = Range("A65536").End(xlUp).Row
Set Rng = Range("A1:W" & Rw)

With Rng
.AutoFilter
.AutoFilter Field:=20, Criteria1:=MyFilter1
.AutoFilter Field:=2, Criteria1:=MyFilter2
.AutoFilter Field:=13, Criteria1:=MyFilter3
End With

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