private static Cache<String, SearchArgument> getSargsCache(Configuration conf) {
    return sargsCache == null? initializeAndGetSargsCache(conf) : sargsCache;
  }
Do the recursive parse of the Hive ExprNodeDesc into our ExpressionTree.
@param expression the Hive ExprNodeDesc
ql/src/java/org/apache/hadoop/hive/ql/io/sarg/ConvertAstToSearchArg.java