code: int getTrieSize()  {
          int size = 0;
          try {
              // The trie serialize function returns the size of the data written.
              //    null output stream says give size only, don't actually write anything.
              size = fTrie.serialize(null, true, dm );
          } catch (IOException e) {
              Assert.assrt (false);
          }
          return size;
      }
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