private static Object getLiteral(Configuration conf, ExprNodeGenericFuncDesc expr,
                                   BoxType boxType,
                                   int position) {
    List<ExprNodeDesc> children = expr.getChildren();
    ExprNodeDesc child = children.get(position);
    return getLiteral(conf, child, boxType);
  }
Return the boxed literal at the given position
@param expr the parent node
@param boxType the type of the expression
@param position the child position to check
@return the boxed literal if found otherwise null
ql/src/java/org/apache/hadoop/hive/ql/io/sarg/ConvertAstToSearchArg.java