How to change MergeFace?

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.

SolidworksApi/macros