Add a material to check if air is air, because there are now 3 types of air.

worldedit-core/src/main/java/com/sk89q/worldedit/world/registry/BlockMaterial.java

@@ -24,6 +24,13 @@ package com.sk89q.worldedit.world.registry;
  */
 public interface BlockMaterial {
 
+    /**
+     * Gets if this block is a type of air.
+     *
+     * @return If it's air
+     */
+    boolean isAir();
+
     /**
      * Get whether this block is a full sized cube.
      *

worldedit-core/src/main/java/com/sk89q/worldedit/world/registry/PassthroughBlockMaterial.java

@@ -29,6 +29,15 @@ public class PassthroughBlockMaterial implements BlockMaterial {
         this.blockMaterial = material;
     }
 
+    @Override
+    public boolean isAir() {
+        if (blockMaterial == null) {
+            return false;
+        } else {
+            return blockMaterial.isAir();
+        }
+    }
+
     @Override
     public boolean isFullCube() {
         if (blockMaterial == null) {

worldedit-core/src/main/java/com/sk89q/worldedit/world/registry/SimpleBlockMaterial.java

@@ -21,6 +21,7 @@ package com.sk89q.worldedit.world.registry;
 
 class SimpleBlockMaterial implements BlockMaterial {
 
+    private boolean isAir;
     private boolean fullCube;
     private boolean opaque;
     private boolean powerSource;
@@ -40,6 +41,15 @@ class SimpleBlockMaterial implements BlockMaterial {
     private boolean isTranslucent;
     private boolean hasContainer;
 
+    @Override
+    public boolean isAir() {
+        return this.isAir;
+    }
+
+    public void setIsAir(boolean isAir) {
+        this.isAir = isAir;
+    }
+
     @Override
     public boolean isFullCube() {
         return fullCube;