Paper/nms-patches/ItemEnderEye.patch

--- a/net/minecraft/server/ItemEnderEye.java
+++ b/net/minecraft/server/ItemEnderEye.java
@@ -61,7 +61,11 @@
 
                     entityendersignal.b(itemstack);
                     entityendersignal.a(blockposition);
-                    world.addEntity(entityendersignal);
+                    // CraftBukkit start
+                    if (!world.addEntity(entityendersignal)) {
+                        return new InteractionResultWrapper(EnumInteractionResult.FAIL, itemstack);
+                    }
+                    // CraftBukkit end
                     if (entityhuman instanceof EntityPlayer) {
                         CriterionTriggers.m.a((EntityPlayer) entityhuman, blockposition);
                     }