Various minor

fix undo null sections
fix cancel for certain parallel jobs
optimize schem paste

worldedit-bukkit/src/main/java/com/boydti/fawe/bukkit/adapter/mc1_14/BukkitGetBlocks_1_14.java

@@ -211,7 +211,6 @@ public class BukkitGetBlocks_1_14 extends CharGetBlocks {
     }
 
     private void updateGet(BukkitGetBlocks_1_14 get, Chunk nmsChunk, ChunkSection[] sections, ChunkSection section, char[] arr, int layer) {
-        checkNotNull(arr);
         synchronized (get) {
             if (this.nmsChunk != nmsChunk) {
                 this.nmsChunk = nmsChunk;