You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: simple_aggr_executor.rs
    path of file: ./repos/tikv/components/tidb_query_executors/src
    
    the code of the file until where you have to start completion: // Copyright 2019 TiKV Project Authors. Licensed under Apache-2.0.

//! Simple aggregation is an aggregation that do not have `GROUP BY`s. It is
//! more even more simpler than stream aggregation.

use std::sync::Arc;

use async_trait::async_trait;
use tidb_query_aggr::*;
use tidb_query_common::{storage:
    
    pub fn check_supported(descriptor: &Aggregation) -> Result<()> {
        assert_eq!(descriptor.get_group_by().len(), 0);
        let aggr_definitions = descriptor.get_agg_func();
        if aggr_definitions.is_empty() {
            return Err(other_err!("Aggregation expression is empty"));
        }

        for def in aggr_definitions {
            AllAggrDefinitionParser.check_supported(def)?;
        }
        Ok(())
    }