private static void assertHasFunctionName(OperatorNode<?> ast, String expectedFunctionName) {
        List<String> names = ast.getArgument(0);
        Preconditions.checkArgument(expectedFunctionName.equals(names.get(0)),
                                    "Expected function '%s', got '%s'.",
                                    expectedFunctionName, names.get(0));
    }
The sorting specified in the YQL+ query last parsed.

@return a Sorting instance or null
container-search/src/main/java/com/yahoo/search/yql/YqlParser.java