code: @Override
      @SuppressWarnings("unchecked")
      public ImmutableCollection<V> values() {
          Object[] array = new Object[size];
          int index = 0;
          for (Object object : values) {
              if (object != null) {
                  array[index++] = object;
              }
          }
          return ImmutableList.copyOf((V[]) array);
      }
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