Fix DragonBattle#initiateRespawn not respecting empty crystal lists

paper-server/patches/sources/net/minecraft/world/level/dimension/end/EnderDragonFight.java.patch

@@ -1,5 +1,13 @@
 --- a/net/minecraft/world/level/dimension/end/EnderDragonFight.java
 +++ b/net/minecraft/world/level/dimension/end/EnderDragonFight.java
+@@ -104,6 +_,7 @@
+     public @Nullable DragonRespawnStage respawnStage;
+     private int respawnTime;
+     public List<EntityReference<EndCrystal>> respawnCrystals;
++    public boolean emptyCrystalRespawnAllowed = false; // Paper - Support allowing the dragon to respawn if no crystals are found
+     public static final Codec<EnderDragonFight> CODEC = RecordCodecBuilder.create(
+         i -> i.group(
+                 ExtraCodecs.optionalAlwaysPresentFieldOf(Codec.BOOL, "needs_state_scanning", true).forGetter(fight -> fight.needsStateScanning),
 @@ -160,6 +_,12 @@
          );
          this.dragonEvent.setPlayBossMusic(true).setCreateWorldFog(true);
@@ -13,6 +21,15 @@
          if (this.gateways.isEmpty()) {
              ObjectArrayList<Integer> newGateways = new ObjectArrayList<>(ContiguousSet.create(Range.closedOpen(0, 20), DiscreteDomain.integers()));
              Util.shuffle(newGateways, RandomSource.createThreadLocalInstance(seed));
+@@ -199,7 +_,7 @@
+                     .map(e -> e.getEntity(this.level, EndCrystal.class))
+                     .filter(Objects::nonNull)
+                     .toList();
+-                if (respawnCrystals.isEmpty()) {
++                if (respawnCrystals.isEmpty() && !this.emptyCrystalRespawnAllowed) { // Paper - Support allowing the dragon to respawn if no crystals are found
+                     this.abortRespawnSequence();
+                     return;
+                 }
 @@ -246,9 +_,9 @@
              this.dragonUUID = dragon.getUUID();
              LOGGER.info("Found that there's a dragon still alive ({})", dragon);
@@ -25,6 +42,14 @@
                  this.dragonUUID = null;
              }
          }
+@@ -281,6 +_,7 @@
+         if (stage == DragonRespawnStage.END) {
+             this.respawnStage = null;
+             this.dragonKilled = false;
++            this.emptyCrystalRespawnAllowed = false; // Paper - Support allowing the dragon to respawn if no crystals are found
+             EnderDragon dragon = this.createNewDragon();
+             if (dragon != null) {
+                 for (ServerPlayer player : this.dragonEvent.getPlayers()) {
 @@ -408,12 +_,20 @@
              this.dragonEvent.setVisible(false);
              this.spawnExitPortal(true);
@@ -112,6 +137,14 @@
              }
          }
      }
+@@ -509,6 +_,7 @@
+
+     private void abortRespawnSequence() {
+         LOGGER.debug("Aborting respawn sequence");
++        this.emptyCrystalRespawnAllowed = false; // Paper - Support allowing the dragon to respawn if no crystals are found
+         this.respawnStage = null;
+         this.respawnTime = 0;
+         this.resetSpikeCrystals();
 @@ -520,7 +_,13 @@
          return this.hasPreviouslyKilledDragon;
      }

paper-server/src/main/java/org/bukkit/craftbukkit/boss/CraftDragonBattle.java

@@ -76,7 +76,7 @@ public void initiateRespawn() {
     }
 
     @Override
-    public boolean initiateRespawn(Collection<EnderCrystal> crystals) { // todo doesn't seems to work without crystals
+    public boolean initiateRespawn(Collection<EnderCrystal> crystals) {
         if (this.hasBeenPreviouslyKilled() && this.getRespawnPhase() == RespawnPhase.NONE) {
             // Copy from EnderDragonFight#tryRespawn for generate exit portal if not exists
             if (this.handle.exitPortalLocation == null) {
@@ -94,6 +94,8 @@ public boolean initiateRespawn(Collection<EnderCrystal> crystals) { // todo does
                 return !((CraftWorld) crystal.getWorld()).getHandle().equals(this.handle.level);
             });
 
+            this.handle.emptyCrystalRespawnAllowed = filteredCrystals.isEmpty();
+
             return this.handle.respawnDragon(
                 Lists.transform(filteredCrystals, crystal -> ((CraftEnderCrystal) crystal).getHandle())
             );