Pre-merge piece of #4101

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/util/LRUMap.java

@@ -15,7 +15,7 @@
  * Since Jackson 2.12, there has been pluggable {@link LookupCache} interface which
  * allows users, frameworks, provide their own cache implementations.
  *<p>
- * Snce Jackson 2.14, the implementation
+ * Since Jackson 2.14, the implementation
  *<ul>
  *<li>Evicts the least recently used  entry when max size is reached
  * </li>
@@ -45,6 +45,12 @@ public LRUMap(int initialEntries, int maxEntries)
                 .build();
     }
 
+    // @since 2.16
+    @Override
+    public LookupCache<K,V> emptyCopy() {
+        return new LRUMap<K,V>(_initialEntries, _maxEntries);
+    }
+
     @Override
     public V put(K key, V value) {
         return _map.put(key, value);

src/main/java/com/fasterxml/jackson/databind/util/LookupCache.java

@@ -9,8 +9,20 @@
  *
  * @since 2.12 (for forwards-compatiblity with 3.0)
  */
-public interface LookupCache <K,V>
+public interface LookupCache<K,V>
 {
+    /**
+     * Method needed for creating clones but without contents.
+     *<p>
+     * Default implementation th
+     *
+     * @since 2.16
+     */
+    default LookupCache<K,V> emptyCopy() {
+        throw new UnsupportedOperationException("LookupCache implementation "
+                +getClass().getName()+" does not implement `emptyCopy()`");
+    }
+
     /**
      * @return Number of entries currently in cache: may be approximate, only
      *    to be used for diagnostics, metrics reporting