This is actually the proper solution

src/turfs.rs

@@ -568,14 +568,14 @@ fn update_visuals(src: ByondValue) -> Result<ByondValue> {
 					byond_string!("set_visuals"),
 					&[overlay_types.as_slice().try_into()?],
 				)
-				.wrap_err("Calling set_visuals"))
-		}
-		// If air is not defined or is null, just call set_visuals with no args
-		_ => {
-			return Ok(src
-				.call_id(byond_string!("set_visuals"), &[])
-				.wrap_err("Calling set_visuals with no args"));
+				.wrap_err("Calling set_visuals")?)
 		}
+		// If air is null, clear the visuals
+		Ok(_) => Ok(src
+			.call_id(byond_string!("set_visuals"), &[])
+			.wrap_err("Calling set_visuals with no args")?),
+		// If air is not defined, it must be a closed turf. Do .othing
+		Err(_) => Ok(ByondValue::null()),
 	}
 }