Figure out TInstance=null situation

My basic approach was to do a Find Usages in IntelliJ for TInstance. I added the `@NotNull` annotation to each one, which includes variables, fields, parameters and return types. I then ran Inspect Code with "Constant Conditions & exceptions" (all checkboxes unchecked). This produced a lot of errors that were unrelated (423 may produce NullPointerException warnings), so I exported it to emacs and threw some text manipulation foo to group everything that complained about setting something that was marked as `@NotNull` with a value that was null. I had previously run `Infer Nullity` so there were a handful of irrelevant issues. I then went through those and heavily used "Analyze Data Flow to Here" to figure out when things might be null. There are still some unknowns, but at this point I feel confident in my explanation on `TInstance` but don't think it's worth going through right now and injecting a TInstance.LiteralNull or Parameter or Unknown at this time.

I investigated the Checker Framework, but couldn't get it to produce any valuable results.