Argument not optional, str = - excel

Question

Why when I want to debug, it will error at
If Emp8.Value = True Then
str = "Whatsapp, "
End If
and it will appear;
Argument not optional
Basically what I want to do is, I want to edit data in the user form.
Private Sub cmdEdit_Click()
If Me.Emp1 = "" Then
Call MsgBox("The fields are not complete", vbInformation, "Edit Contact")
Exit Sub
End If
Set findvalue = Sheet1.Range("b8:b10000").Find(What:=Me.Emp1, LookIn:=xlValues)
findvalue.Offset(0, 1).Value = Me.Emp1.Value
If Emp8.Value = True Then
str = "Whatsapp, "
End If
If Emp12.Value = True Then
str = str & "SMS, "
End If
If Emp11.Value = True Then
str = str & "Email, "
End If
If Emp10.Value = True Then
str = str & "Facebook, "
End If
If Emp9.Value = True Then
str = str & "Phone Call, "
End If
str = Left(str, Len(str) - 2)
findvalue.Offset(0, 2) = str
If Emp2.Value = True Then
findvalue.Offset(0, 3) = "Yes"
ElseIf Emp3.Value = True Then
findvalue.Offset(0, 3) = "No"
End If
findvalue.Offset(0, 4).Value = Me.Emp4.Value
findvalue.Offset(0, 5).Value = Me.Emp5.Value
findvalue.Offset(0, 6).Value = Me.Emp6.Value
findvalue.Offset(0, 7).Value = Me.Emp7.Value
Call MsgBox("The contact has been updated", vbInformation, "Edit Contact")
On Error GoTo 0
Exit Sub
End Sub