private void createLeaf(PredicateLeaf.Operator operator,
                          ExprNodeGenericFuncDesc expression) {
    createLeaf(operator, expression, findVariable(expression));
  }
Create a leaf expression when we aren't sure where the variable is
located.
@param operator the operator type that was found
@param expression the expression to check
ql/src/java/org/apache/hadoop/hive/ql/io/sarg/ConvertAstToSearchArg.java