GetDatasourceDependencies checks for all the dependencies.
In the background it uses LinkDatabase to get all the referrers and referred items.
If there is an item link in the LinkDatabase but the items from the link are no longer in database, it may result in null reference exception.
Solution: rebuild the link database.
Spellchecking lucene algorithms are many times smarter than just "calculate edit distance between term and all possible combinations of indexed word", because of perfomance.
First character in term is very important in spellchecking, also because of performance, and I recommend you do not use minPrefix=0 setting that disabled first character ...