Yeah i know, its the base thats odd, the only reason your getting errors from explosions is probobly from a wierdo addon you have, coz i dont get any errors at all, and i downloaded it and removed my addons with jsut adding this.
I recreated the problem I mentioned:
Timer Error: entities/sin_grenade/init.lua:20: Tried to use a NULL entity!
Timer Error: entities/sin_grenade/init.lua:16: Tried to use a NULL entity!
Timer Error: entities/sin_grenade/init.lua:12: Tried to use a NULL entity!
Timer Error: entities/sin_grenade/init.lua:8: Tried to use a NULL entity!
Throw two grenades right next to each other. When the first one detonates, the second grenade will just vanish and the console will be spammed with these errors.