What is your Joomla version ?
This error comes from the call of queryDump()
// FROM
$obj->FROM = $query->from->getElements()[0];
Where do you use it ?
queryDump() is interracting with a Joomla Query class, so I guess on a retrograde version it is different. I need to know your Joomla version in order to be able to do the fix.
You can also try by yourself in the queryDump() function. (ORM Class file)
Dump the Joolma Query object and extract the SELECT statement as it should normaly do.
I tested on last 3.6.5 and it works perfectly.
Try again, I have written some variable checks to protect against fatal, but it would certainly not fix your problem.
I cannot say more at the moment.
Check and re-check your tests. because first of all, you may be using queryDump() to enter on that line, so that's strange.