code: private SemanticVector getSemanticVector(String word) {
          SemanticVector v = wordToMeaning.get(word);
          if (v == null) {
              v = (useSparseSemantics) 
                  ? new SparseSemanticVector(vectorLength)
                  : new DenseSemanticVector(vectorLength);
              wordToMeaning.put(word, v);
          }
          return v;
      }
docs: Returns the current semantic vector for the provided word, or if the word
  is not currently in the semantic space, a vector is added for it and
  returned.
  
  @param word a word
  
  @return the {@code SemanticVector} for the provide word.