1 files changed, 12 insertions, 6 deletions

diff --git a/src/utils/lombok/javac/TreeMirrorMaker.java b/src/utils/lombok/javac/TreeMirrorMaker.java
index 778e670d..44e26ab6 100644
--- a/src/utils/lombok/javac/TreeMirrorMaker.java
+++ b/src/utils/lombok/javac/TreeMirrorMaker.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2010-2015 The Project Lombok Authors.
+ * Copyright (C) 2010-2021 The Project Lombok Authors.
  * 
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -58,14 +58,14 @@ public class TreeMirrorMaker extends TreeCopier<Void> {
 	
 	@Override public <T extends JCTree> T copy(T original) {
 		T copy = super.copy(original);
-		originalToCopy.put(original, copy);
+		putIfAbsent(originalToCopy, original, copy);
 		return copy;
 	}
 	
 	@Override public <T extends JCTree> T copy(T original, Void p) {
 		T copy = super.copy(original, p);
-		originalToCopy.put(original, copy);
-		return copy;
+		putIfAbsent(originalToCopy, original, copy);
+		return copy; 
 	}
 	
 	@Override public <T extends JCTree> List<T> copy(List<T> originals) {
@@ -73,7 +73,7 @@ public class TreeMirrorMaker extends TreeCopier<Void> {
 		if (originals != null) {
 			Iterator<T> it1 = originals.iterator();
 			Iterator<T> it2 = copies.iterator();
-			while (it1.hasNext()) originalToCopy.put(it1.next(), it2.next());
+			while (it1.hasNext()) putIfAbsent(originalToCopy, it1.next(), it2.next());
 		}
 		return copies;
 	}
@@ -83,7 +83,7 @@ public class TreeMirrorMaker extends TreeCopier<Void> {
 		if (originals != null) {
 			Iterator<T> it1 = originals.iterator();
 			Iterator<T> it2 = copies.iterator();
-			while (it1.hasNext()) originalToCopy.put(it1.next(), it2.next());
+			while (it1.hasNext()) putIfAbsent(originalToCopy, it1.next(), it2.next());
 		}
 		return copies;
 	}
@@ -137,4 +137,10 @@ public class TreeMirrorMaker extends TreeCopier<Void> {
 	@Override public JCTree visitLabeledStatement(LabeledStatementTree node, Void p) {
 		return node.getStatement().accept(this, p);
 	}
+	
+	private <K, V> void putIfAbsent(Map<K, V> map, K key, V value) {
+		if (!map.containsKey(key)) {
+			map.put(key, value);
+		}
+	}
 }