PaperMC/paper-server/nms-patches/net/minecraft/world/entity/projectile/EntityEnderSignal.patch

--- a/net/minecraft/world/entity/projectile/EntityEnderSignal.java
+++ b/net/minecraft/world/entity/projectile/EntityEnderSignal.java
@@ -35,7 +35,7 @@
     }
 
     public void setItem(ItemStack itemstack) {
-        if (!itemstack.is(Items.ENDER_EYE) || itemstack.hasTag()) {
+        if (true || !itemstack.is(Items.ENDER_EYE) || itemstack.hasTag()) { // CraftBukkit - always allow item changing
             this.getEntityData().set(EntityEnderSignal.DATA_ITEM_STACK, itemstack.copyWithCount(1));
         }
 
@@ -177,7 +177,7 @@
     public void readAdditionalSaveData(NBTTagCompound nbttagcompound) {
         ItemStack itemstack = ItemStack.of(nbttagcompound.getCompound("Item"));
 
-        this.setItem(itemstack);
+        if (!itemstack.isEmpty()) this.setItem(itemstack); // CraftBukkit - SPIGOT-6103 summon, see also SPIGOT-5474
     }
 
     @Override