Trying to view lab information after respective modules are deleted results in NullPointer

Summary

Exactly what the title says.

Steps to reproduce

1. Delete modules that an existing lab uses.
2. Try to edit the lab as a teacher or go to the lab information page as a student.

Possible Fix

Get rid of existing module references when it is deleted, such as ALL associated assignments.

Logs

java.lang.NullPointerException: Cannot invoke "nl.tudelft.labracore.api.dto.AssignmentDetailsDTO.getModule()" because "a" is null at nl.tudelft.queue.controller.LabController.lambda$setEnqueuePageAttributes$4(LabController.java:685) at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:178) at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625) at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509) at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499) at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:575) at java.base/java.util.stream.AbstractPipeline.evaluateToArrayNode(AbstractPipeline.java:260) at java.base/java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:616) at java.base/java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:622) at java.base/java.util.stream.ReferencePipeline.toList(ReferencePipeline.java:627) at nl.tudelft.queue.controller.LabController.setEnqueuePageAttributes(LabController.java:688) at nl.tudelft.queue.controller.LabController.getSessionView(LabController.java:136)