Forge: 14.23.5.2772
YUNoMakeGoodMap: 1.12-6.3.0.29
On 1.12.2 when I set the server.properties level-name to void the world still generates with generatorName: default. Moving a world that has generatorName: void in level.dat works properly so I am guessing that the server just does not register the void level type early enough when it is looking for the generator from server.properties