C#: Use of unassigned local variable, using a foreach and if

Initialize result when you declare it. If the collection is empty neither of the branches of the if statement will ever be taken and result will never be assigned before it is returned.

public string return_Result(String[,] RssData, int marketId)
{
    string result = "";
    foreach (var item in RssData)
    {
        if (item.ToString() == marketId.ToString())
        {
            result = item.ToString();
        }
    }
    return result;
}