How to override ExecuteQueryAsync method?

[kgiddu]

I am trying to support Oracle database and I cannot seem to be table to override the ExecuteQueryAsync method in OracleQueryExecutor. cs

Class definition: public class OracleQueryExecutor : QueryExecutor

    public override async Task<TResult?> ExecuteQueryAsync<TResult>(
        string sqltext,
        IDictionary<string, DbConnectionParam> parameters,
        Func<DbDataReader, List<string>?, Task<TResult>>? dataReaderHandler,
        string dataSourceName,
        HttpContext? httpContext = null,
        List<string>? args = null)
    {
       // Execute Oracle specific queries if not call base. 
       
        TResult? result = await base.ExecuteQueryAsync(
            sqltext,
            parameters,
            dataReaderHandler,
            dataSourceName,
            httpContext,
            args);

        return result;
    }

I get this error
'OracleQueryExecutor.ExecuteQueryAsync(string, IDictionary<string, DbConnectionParam>, Func<DbDataReader, List?, Task>?, string, HttpContext?, List?)': return type must be 'Task<TResult?>' to match overridden member 'QueryExecutor.ExecuteQueryAsync(string, IDictionary<string, DbConnectionParam>, Func<DbDataReader, List?, Task>?, string, HttpContext?, List?)'

Tried this as well
public override async Task<TResult?> ExecuteQueryAsync(
string sqltext,
IDictionary<string, DbConnectionParam> parameters,
Func<DbDataReader, List?, Task>? dataReaderHandler,
string dataSourceName,
HttpContext? httpContext = null,
List? args = null)
{
TResult? result = default(TResult);

        return result;
    }

Got this error
Cannot implicitly convert type 'TResult' to 'TResult?'. An explicit conversion exists (are you missing a cast?)