How to check if string is null in c#.net
<p>I am reading text file in c#.net 
at the end one line is completely null but in foreach c# can not detect null string so It gets error </p>

<pre><code>string[] lines = System.IO.File.ReadAllLines(dir);
List&lt;KeyValuePair&lt;int, DateTime&gt;&gt; items = new List&lt;KeyValuePair&lt;int, DateTime&gt;&gt;();
List&lt;KeyValuePair&lt;int, DateTime&gt;&gt; lst = new List&lt;KeyValuePair&lt;int, DateTime&gt;&gt;();
foreach (string line in lines)
{
    if (line!=string.Empty)
    {
        l = line.Split('\t');
        l[0] = l[0].Trim();
        PersianCalendar persCal = new PersianCalendar();
        SqlConnection sqlconn = new SqlConnection(DBsetting.Connstring);
        SqlCommand sqlda = new SqlCommand("InsertReadd", sqlconn);
        sqlda.CommandType = CommandType.StoredProcedure;
        sqlda.Parameters.AddWithValue("@date", l[1]);
        sqlda.Parameters.AddWithValue("@IDp", l[0]);
        sqlda.Parameters.AddWithValue("@day", GetDayOfWeek(GetPerDate(l[1])));
        sqlda.Parameters.AddWithValue("@nobatkari", "");
        sqlda.Connection.Open();
        sqlda.ExecuteNonQuery();
        sqlda.Connection.Close();
    }
}
RefGrid();
</code></pre>