code: public Object remove(Object key) {
          if (key instanceof Number) {
              return remove( ((Number)key).intValue() );
          }
          else {
              return null;
          }
      }
docs: Removes the mapping for this key from this map if present.
  
  @param key key whose mapping is to be removed from the map.
  @return previous value associated with specified key, or <tt>null</tt>
  if there was no mapping for key.  A <tt>null</tt> return can
  also indicate that the map previously associated <tt>null</tt>
  with the specified key.