In The Mandalorian season 2, episode 4, "Chapter 12: The Siege", an old Star Wars joke about the Empire's lack of guard rails makes it into canon. While the Empire has been defeated for a few years by the point in the timeline The Mandalorian takes places, there is still a strong Imperial Remnant that ensures its presence remains. That comes to the fore in "The Siege", which sees Mando teaming-up with Greef Karga, Cara Dune, and the Mythrol to infiltrate an old Imperial base on Nevarro.
Much of The Mandalorian season 2, episode 4 feels like an homage to Star Wars: A New Hope, which is compounded when the Mythrol has to drain the coolant lines using the reactor controls, allowing the lava underneath to explode upwards and destroy the base. The control panel and the way the Mythrol moves around it are extremely similar in design to Obi-Wan Kenobi on the Death Star's tractor beam terminal in A New Hope, and so, fittingly enough, this is where the joke comes into play.
When told he has to climb around the reactor controls, which sit above a bed of lava, the Mythrol resists, exclaiming that: "There's no guard rail on this." Aside from in keeping with the aesthetic of the tractor beam terminal, it's a joke that Star Wars fans have been making ever since 1977, when Obi-Wan himself had to make the risky mission. That was the first look at the complete absence of safety railings in Star Wars, but there have been many more since. The Death Star itself was missing many more in places that needed them, and other notable examples include the landing bay on Bespin in The Empire Strikes Back, the Theed power generator where Obi-Wan and Qui-Gon Jinn duelled Darth Maul in Star Wars: Episode I - The Phantom Menace, various walkways on Coruscant, and the one on Starkiller Base where Han Solo is killed in Star Wars: The Force Awakens.
Fans have long enjoyed pointing this out and questioning perhaps why it is the case. The gag even made it into Seth MacFarlane's Family Guy Star Wars parodies, with Blue Harvest showing two Death Star workers complaining about the lack of railings while above a vast pit that could easily be fallen down. Noting that they've almost tripped and fell down it many a time and that they've voiced their complaints, the movie offers the answer that the Empire is "worried we'd be leaning all day." While all part of the joke, it would fit with the ruthlessness of the Empire to treat their workers in such a way, not wishing to give them any chances to take a break or slack off, and nor would they think their safety would be of any actual importance.
Although not previously addressed in canon, there is an answer as to why there are no guard rails in Star Wars from George Lucas himself. In an interview with The Star Wars Show, Rogue One production designer Doug Chiang addressed the lack of safety railings, saying: "You know, that’s the funny thing. It's one of those iconic things that George wanted to establish in the Star Wars locale, that there’s no health and safety. It’s this crazy thing where the minute you take away handrails or anything like that, it really kind of puts it in the Star Wars world."
The Star Wars universe isn't completely without guard rails - there are some on Bespin where Darth Vader and Luke Skywalker duel, and around the reactor core on the second Death Star (though ironically neither made much of a difference in the end) - but the absence of them is noteworthy enough to have been pointed out by fans across the years, and now The Mandalorian season 2 gets in on the act as well. It's a funny, loving bit of fan-service that continues to show just how well the producers get Star Wars, and while it's a shame that healthy and safety still hasn't improved in the galaxy, it's great to see the joke referenced.