compile flora addon

common/api/src/main/java/com/dfsek/terra/api/util/MaterialSet.java

@@ -2,7 +2,11 @@ package com.dfsek.terra.api.util;
 
 import com.dfsek.terra.api.block.BlockType;
 
+import java.util.Collections;
 import java.util.Set;
 
 public interface MaterialSet extends Set<BlockType> {
+    static MaterialSet empty() {
+        return (MaterialSet) (Object) Collections.emptySet();
+    }
 }