Engine Error at random point

Just had this pop up after I started building a template building.
Steps to reproduce:
didn’t happen the first time so don’t think it is actually related to the building project but an item that is being used in the project.
Expected Results:

Actual Results:
Can’t see anything that isn’t where it is supposed to be or that is actually broken just see the error report
This is the second time I have gotten this error and both times I have not notice anything actually wrong but I always have 2-5 things going on at a time so it could be a person crafting, a person building, a person farming, or a person mining but I don’t know which. The first time this happened was on another game in which I maxed the population at 20 before I got the message.
Error Message:
release-549 (x64)
…onehearth/components/building/building_component.lua:586: attempt to index a nil value
stack traceback:
radiant/modules/common.lua:223: in function 'report_traceback’
radiant/modules/common.lua:234: in function <radiant/modules/common.lua:228>
…onehearth/components/building/building_component.lua:586: in function ‘_on_child_finished’
…onehearth/components/building/building_component.lua:322: in function 'instance’
radiant/modules/events.lua:206: in function <radiant/modules/events.lua:200>
[C]: in function 'xpcall’
radiant/modules/common.lua:243: in function 'xpcall’
radiant/modules/events.lua:200: in function 'trigger’
radiant/modules/events.lua:241: in function '_fire_async_triggers’
radiant/modules/events.lua:319: in function '_update’
radiant/server.lua:62: in function <radiant/server.lua:58>
Version Number and Mods in use:
System Information:
Windows 10 Pro
Nvidia Geforce GT 730 driver vs. 364.72
Screen Resoultion 1600x900 60Hz
Intel i7-3770 CPU 3.4GHz