v2.5.3: added a safety check for spectral necromancer summoning

core/src/main/java/com/shatteredpixel/shatteredpixeldungeon/actors/mobs/SpectralNecromancer.java

@@ -152,6 +152,10 @@ public class SpectralNecromancer extends Necromancer {
 		summoning = firstSummon = false;
 
 		Wraith wraith = Wraith.spawnAt(summoningPos, Wraith.class);
+		if (wraith == null){
+			spend(TICK);
+			return;
+		}
 		wraith.adjustStats(0);
 		Dungeon.level.occupyCell( wraith );
 		((SpectralNecromancerSprite)sprite).finishSummoning();