Fix handling of empty strings passed to Block/ItemType

src/main/java/com/sk89q/worldedit/blocks/BlockType.java

@@ -237,6 +237,10 @@ public enum BlockType {
     public static BlockType lookup(String name, boolean fuzzy) {
         String testName = name.replace(" ", "").toLowerCase();
         
+        if (testName.length() == 0) {
+            return null;
+        }
+
         BlockType type = lookup.get(testName);
 
         if (type != null) {

src/main/java/com/sk89q/worldedit/blocks/ItemType.java

@@ -415,6 +415,10 @@ public enum ItemType {
     public static ItemType lookup(String name, boolean fuzzy) {
         String testName = name.replace(" ", "").toLowerCase();
         
+        if (testName.length() == 0) {
+            return null;
+        }
+
         ItemType type = lookup.get(testName);
 
         if (type != null) {