External   |  
 The assembly path of the menu item. 
 Namespace: Autodesk.Revit.UI
Assembly: RevitAPIUI (in RevitAPIUI.dll) Version: 25.0.0.0 (25.0.0.0)
| Exception | Condition | 
|---|---|
| ArgumentNullException | When setting this property: A non-optional argument was null | 
 The path of the assembly which contains the corresponding external command.