Fixed #4128

core/src/mindustry/input/InputHandler.java

@@ -110,7 +110,9 @@ public abstract class InputHandler implements InputProcessor, GestureListener{
         for(int i = 0; i < Mathf.clamp(amount / 3, 1, 8); i++){
             Time.run(i * 3, () -> createItemTransfer(item, amount, x, y, build, () -> {}));
         }
-        build.handleStack(item, amount, unit);
+        if(amount > 0){
+            build.handleStack(item, amount, unit);
+        }
     }
 
     public static void createItemTransfer(Item item, int amount, float x, float y, Position to, Runnable done){

core/src/mindustry/world/blocks/distribution/StackConveyor.java

@@ -266,6 +266,7 @@ public class StackConveyor extends Block implements Autotiler{
 
         @Override
         public void handleStack(Item item, int amount, Teamc source){
+            if(amount <= 0) return;
             if(items.empty()) poofIn();
             super.handleStack(item, amount, source);
             lastItem = item;