When deleting XPages watch your form property "Display XPage instead"

During the XPages training in Manila we found an interesting behaviour of the "Display XPage instead" property of a form. To reproduce this follow these steps:

1. Create a form form1
2. Create an XPage test1.xsp
3. Set the form property "Display XPage instead" (both for Client and web) to test1.xsp
4. Preview form1 in Notes client and web - works as designed, test1.xsp will show.
5. Now delete test1.xsp
6. Preview form1 in Notes client and web - it will show an error
7. Inspect the "Display XPage instead" property of form1: it will show empty since test1.xsp is no longer a selectable item, However that value is still stored in the form (we didn't touch it at this point)
8. Open the form1 as DXL. At the end of the form you will find:
   <item name='$XPageAlt'><text>test1.xsp </text></item>
   <item name='$XPageAltClient'><text>test1.xsp </text></item>
9. To fix this: Either delete the lines in DXL (if you dare ) - or: in the form property "Display XPage instead" select any other XPage (optional) and then the empty item on top and save the form. Just open and save the form doesn't do the trick, you have to touch the form property

Nice one