sql - Can't check null value with these 2 ways C# datareader Null value Error -

the problem ; use code inside class , call class main form. got error datareader cant null value. how can check coming data sp not null. inside code if see null change , return outval (0000)

public string opt() {    string strng= "";    string outval= "";    sqlconnection conn = new sqlconnection();    conn.connectionstring = configurationmanager.connectionstrings["nmrbg"].connectionstring;    conn.open();    sqlcommand cmd = new sqlcommand("nmp_sp_sy", conn);    cmd.commandtype = commandtype.storedprocedure;    sqldatareader rdr = cmd.executereader();        // if (rdr.hasrows)    // {    //     while (rdr.read())    //     {    //        int nm= rdr.getint32(0);    //        strng= convert.tostring(nm);    //        outval= strng;    //     }    // }    while (rdr.read())    {       int nm= rdr.getint32(0);       strng= convert.tostring(nm);       outval= strng;    }    if (!rdr.hasrows)    {       outval= "0000";    }    rdr.close();    rdr.dispose();    conn.close();    conn.dispose();    return outval; } 

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sp ;

begin      begin transaction     declare @minsira int      select  @minsira=min(sirano)      nmr_tbl_srbklynlr      turid=2 , aktifpasif=1      update top (1) nmr_tbl_srbklynlr     set aktifpasif = 0     sirano=@minsira      select @minsira     commit transaction  end 

test returning values on null: database return null on int. wrap idisposable using: prevents resource leakage on both normal flow , exceptions.

public string opt() {   using (sqlconnection conn = new sqlconnection(configurationmanager.connectionstrings["nmrbg"].connectionstring)) {     conn.open();      using (sqlcommand cmd = new sqlcommand("nmp_sp_sy", conn)) {       cmd.commandtype = commandtype.storedprocedure;        using (sqldatareader rdr = cmd.executereader()) {         // if there's no records read (rdr empty) return default         if (!rdr.read())           return "0000";          object rawdata = rdr.getvalue(0);          if (object.refrenceequals(null, rawdata))             return "0000"; // <- or whatever on null value         else           return rawdata.tostring();           }     }   } }