private static ExpressionTree makeExpressionTree(String filter) throws MetaException {
    // TODO: ExprNodeDesc is an expression tree, we could just use that and be rid of Filter.g.
    if (filter == null || filter.isEmpty()) {
      return ExpressionTree.EMPTY_TREE;
    }
    LOG.debug("Filter specified is " + filter);
    ExpressionTree tree = null;
    try {
      tree = parseFilterTree(filter);
    } catch (MetaException ex) {
      LOG.info("Unable to make the expression tree from expression string ["
          + filter + "]" + ex.getMessage()); // Don't log the stack, this is normal.
    }
    return tree;
  }
Makes expression tree out of expr.
@param filter Filter.
@return Expression tree. Null if there was an error.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/PartFilterExprUtil.java