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: receive.rs
    path of file: ./repos/holochain-rust/crates/core/src/wasm_engine/callback
    
    the code of the file until where you have to start completion: use crate::{
    context::Context,
    nucleus::CallbackFnCall,
    wasm_engine::{
        self,
        callback::{Callback, CallbackParams, CallbackResult},
        runtime::WasmCallData,
        Defn,
    },
};

use holochain_json_api::{error::JsonError, json::JsonString};
use std::sync::Arc;

#[derive(Serialize, Deserialize, Debug, DefaultJson)]
struct ReceiveReturnValue(Result<String, String>);

#[autotrace]
#[holochain_traci
    
    fn implemented_with_null() {
        let zome = "test_zome";
        let netname = Some("implemented_with_null");
        let instance = test_callback_instance(zome, Callback::Receive.as_str(), 0, netname)
            .expect("Test callback instance could not be initialized");
        let context = instance.initialize_context(test_context("test", netname));

        let result = receive(
            context,
            zome,
            &CallbackParams::Receive(ReceiveParams {
                from: Address::from(""),
                payload: String::from(""),
            }),
        );

        assert_eq!(CallbackResult::ReceiveResult(String::from("null")), result);
    }