code: public void putAll(Map<? extends Pair<K, T>, ? extends V> m) {
          backedMap.putAll(m);
      }
docs: Copies all of the mappings from the specified map to this map
  (optional operation).  The effect of this call is equivalent to that
  of calling {@link Map<>#put(k, v)} on this map once
  for each mapping from key <tt>k</tt> to value <tt>v</tt> in the
  specified map.  The behavior of this operation is undefined if the
  specified map is modified while the operation is in progress.
  
  @param m mappings to be stored in this map
  @throws UnsupportedOperationException if the <tt>putAll</tt> operation
  is not supported by this map
  @throws ClassCastException            if the class of a key or value in the
  specified map prevents it from being stored in this map
  @throws NullPointerException          if the specified map is null, or if
  this map does not permit null keys or values, and the
  specified map contains null keys or values
  @throws IllegalArgumentException      if some property of a key or value in
  the specified map prevents it from being stored in this map