Server error 500 when attempting to delete knowledge statement in admin interface

[stappan]

Version: 3.2.0
Process to replicate:

1. Search for sentence: https://composer.scicrunch.io/sentence/659
2. select tab for connectivity statements.
3. first entry, statement 287, is empty of text and references because i tried to delete it from the front end
4. Select red check box in upper right corner.
5. select save.
   Server Error 500
   https://composer.scicrunch.io/admin/composer/sentence/659/change/?_changelist_filters=q%3DThe%2Benteric%2Bnervous%2Bsystem%2Bis%2Bthe%2Blargest%2Band%2Bmost%2Bcomplex%2Bunit%2Bof%2Bthe%2Bperipheral%2Bnervous%2Bsystem%252C%2Bwith%2B~600%2Bmillion%2Bneurons%2Breleasing%2Ba%2Bmultitude%2Bof%2Bneurotransmitters%2Bto%2Bfacilitate%2Bthe%2Bmotor%252C%2Bsensory%252C%2Babsorptive%252C%2Band%2Bsecretory%2Bfunctions%2Bof%2Bthe%2Bgastrointestinal%2Btract.

Note: issue happens as written even if text & refs are available

[stappan]

Note: When this bug happens, the origins of all affiliated statements are deleted from the path builder.