rpc: Audit contract reader returns error from `List` when contract has no items

im exploring Audit contract in public NeoFS networks. I called list method of the Audit contract to analyze all stored results. As it turned out, there are no results in the contract, but I found out about this in an unexpected way

Current Behavior

Error:          Received unexpected error:
                            not an array

Expected Behavior

no error and number of results: 0

Possible Solution

i dug down to the result stack: there is 1 element of type Null. The error is originated by https://pkg.go.dev/github.com/nspcc-dev/neo-go@v0.106.2/pkg/rpcclient/unwrap#Array

i see next alternatives:

make unwrap.Array to return nil, nil
make unwrap.Array to return ErrNull
add new function ArrayOrNull
do manual stack surgery

being a user, i like 1 the most, but this is a change that could break some code which also treats null as an error. 3 will prevent this, but there is a whole family of ArrayOf* functions, and generated code . 4 is the worst to me - unwrap package and generated RPC callers were conceived to avoid this

another challenge is to teach codegen what to do - fail or not on null

Steps to Reproduce

func TestAuditResults(t *testing.T) {
    h, err := util.Uint160DecodeStringLE("85fe181f4aa3cbdc94023d97c69001ece0730398")
    require.NoError(t, err)
    c, err := rpcclient.New(context.Background(), "https://rpc1.morph.fs.neo.org:40341", rpcclient.Options{})
    require.NoError(t, err)
    require.NoError(t, c.Init())

    list, err := auditcontract.NewReader(invoker.New(c, nil), h).List()
    require.NoError(t, err)
    fmt.Println("number of results:", len(list))
}

Context

there are some other contracts and/or methods returning arrays, so same issue is likely related to them

Regression

Your Environment

github.com/nspcc-dev/neo-go@v0.106.2
github.com/nspcc-dev/neofs-contract@v0.19.2-0.20240621202015-9293f8749928 (latest)

P.S.

i'd add context to the error, who is not an array, of course you can guess, but you can also doubt it

nspcc-dev / neofs-contract