Improved replacement system

core/src/mindustry/world/modules/ItemModule.java

@@ -180,6 +180,7 @@ public class ItemModule extends BlockModule{
         return total > 0;
     }
 
+    @Nullable
     public Item first(){
         for(int i = 0; i < items.length; i++){
             if(items[i] > 0){
@@ -189,6 +190,7 @@ public class ItemModule extends BlockModule{
         return null;
     }
 
+    @Nullable
     public Item take(){
         for(int i = 0; i < items.length; i++){
             int index = (i + takeRotation);
@@ -204,6 +206,7 @@ public class ItemModule extends BlockModule{
     }
 
     /** Begins a speculative take operation. This returns the item that would be returned by #take(), but does not change state. */
+    @Nullable
     public Item beginTake(){
         for(int i = 0; i < items.length; i++){
             int index = (i + takeRotation);