Merge: Minor Improvements to the Parallelisation Phase

Support modules without a module declaration and nullable types in threaded methods.

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Don't worry, it's the last PR for today and my dev branches are getting short.

Pull-Request: #1546
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>