I've trying to make a macro that switches the "merge faces" option to "True" in sheet metal flat patterns. However, I keep getting a Run-time error 91. I think I set all of the objects but maybe I'm missing something obvious.

Option Explicit
Dim swApp           As Object
Dim swModelDoc      As SldWorks.ModelDoc2
Dim swFlatPattern   As SldWorks.FlatPatternFeatureData
Dim swFeat          As SldWorks.Feature
Dim swModel         As SldWorks.ModelDoc2
Sub main()
    Set swApp = Application.SldWorks
    Set swModelDoc = swApp.ActiveDoc
    
    Set swFeat = swModel.FirstFeature
    Set swFlatPattern = swFeat.GetDefinition
    
    swFlatPattern.MergeFace = True
    
End Sub

EDIT: This is supposed to run on an already-open sheet metal part.