Event-based synthesis should allow specifications without requirements
Currently, the event-based synthesis pre-checker fails specifications without any requirement automaton. Theoretically, synthesis can also be performed just on plant automata. This situation can arise when one, for example, first performs plantification of the requirements.
Looking at the actual implementation of event-based synthesis, I don't see any reason why an empty set of requirements is problematic. A quick test on a model without requirements and removing the check resulting in the expected result, so the code can actually synthesize a supervisor for a specification without requirements.