code: public boolean putIfAbsent(KType key, VType value) {
      int keyIndex = indexOf(key);
      if (!indexExists(keyIndex)) {
        indexInsert(keyIndex, key, value);
        return true;
      } else {
        return false;
      }
    }
docs: <a href="http://trove4j.sourceforge.net">Trove</a>-inspired API method. An equivalent
  of the following code:
  <pre>
  if (!map.containsKey(key)) map.put(value);
  </pre>
  
  @param key The key of the value to check.
  @param value The value to put if <code>key</code> does not exist.
  @return <code>true</code> if <code>key</code> did not exist and <code>value</code>
  was placed in the map.