private AggCall getAggCall(Expression aggregateExpression) {
            if (isFunctionOfKind(aggregateExpression, TABLE_AGGREGATE)) {
                return aggregateExpression.accept(tableAggregateVisitor);
            } else {
                return aggregateExpression.accept(aggregateVisitor);
            }
        }
Get the {@link AggCall} correspond to the aggregate or table aggregate expression.
core/src/main/java/org/apache/flink/table/planner/plan/QueryOperationConverter.java