Like a noob, I missed some things... broke the compilation.

classpath/java/util/IdentityHashMap.java

@@ -37,7 +37,7 @@ public class IdentityHashMap<K, V> implements Map<K, V> {
     return map.containsValue(value);
   }
 
-  public V get(K key) {
+  public V get(Object key) {
     return map.get(key);
   }
 
@@ -49,7 +49,7 @@ public class IdentityHashMap<K, V> implements Map<K, V> {
     map.putAll(elts);
   }
 
-  public V remove(K key) {
+  public V remove(Object key) {
     return map.remove(key);
   }