code: @FFDCIgnore(IllegalArgumentException.class)
      public boolean putIfAbsent(K key, E element) {
          try {
              put(key, element);
              return true;
          } catch (IllegalArgumentException e) {
              return false;
          }
      }
docs: Add the element associated with the given key into the list at the established position for that key.
  
  @param key the key to use to add the element, which must match one of the keys provided to the constructor
  @param element the element to add
  @return <code>true</code> if the element was added and <code>false</code> otherwise