Paper/paper-server/nms-patches/net/minecraft/world/item/ItemEndCrystal.patch

--- a/net/minecraft/world/item/ItemEndCrystal.java
+++ b/net/minecraft/world/item/ItemEndCrystal.java
@@ -45,6 +45,11 @@
                         EntityEnderCrystal entityendercrystal = new EntityEnderCrystal(world, d0 + 0.5D, d1, d2 + 0.5D);
 
                         entityendercrystal.setShowingBottom(false);
+                        // CraftBukkit start
+                        if (org.bukkit.craftbukkit.event.CraftEventFactory.callEntityPlaceEvent(itemactioncontext, entityendercrystal).isCancelled()) {
+                            return EnumInteractionResult.FAIL;
+                        }
+                        // CraftBukkit end
                         world.addEntity(entityendercrystal);
                         EnderDragonBattle enderdragonbattle = ((WorldServer) world).getDragonBattle();