Gets or sets the URL of the master page that is used for the Web site.
Assembly: Microsoft.SharePoint (in Microsoft.SharePoint.dll)
The and CustomMasterUrl properties are both set to "/_catalogs/masterpage/default.master" by default. If you subsequently need to delete the default.master file, you must set both of those properties to a different value. If you set just one of them to a different value, an error is raised that suggests that the default.master file is still being used as the master page for the site.