code: @Override
      public void _boost(double boost) {
          if (boost == 1.0) {
              return;
          }
  
          List<QueryToken> tokens = getCurrentWhereTokens();
          if (tokens.isEmpty()) {
              throw new IllegalStateException("Missing where clause");
          }
  
          QueryToken whereToken = tokens.get(tokens.size() - 1);
          if (!(whereToken instanceof WhereToken)) {
              throw new IllegalStateException("Missing where clause");
          }
  
          if (boost < 0.0) {
              throw new IllegalArgumentException("Boost factor must be a non-negative number");
          }
  
          ((WhereToken) whereToken).getOptions().setBoost(boost);
      }
docs: Specifies a boost weight to the last where clause.
  The higher the boost factor, the more relevant the term will be.
  <p>
  boosting factor where 1.0 is default, less than 1.0 is lower weight, greater than 1.0 is higher weight
  <p>
  http://lucene.apache.org/java/2_4_0/queryparsersyntax.html#Boosting%20a%20Term
  
  @param boost Boost value