how to INSERT a NULL value in mysql, taken from a variable. ASP

[mumblez]

lets assume i have a staement variable like this:\[code\]sql_ins = "INSERT INTO tableName (field1,field2,field3) VALUES ("&var1&","&var2&","&var3&")\[/code\]well, let's say that var1, var2, var3 could be also \[code\]null\[/code\], and the database has default values as \[code\]null\[/code\].the problem is that i could insert a \[code\]NULL\[/code\] value, but if the variable is \[code\]null\[/code\] it will be empty, so the sql_ins should look like:\[code\]INSERT INTO tableName (field1,field2,field3) VALUES (4,,)\[/code\]how i could avoid it?thanks in advance.real code here:\[code\]For Each Field in Request.Form TheString = Field & "=Request.Form(""" _ & Field & """)" EXECUTE(TheString)Nextif imm_id <> "" then'TODO modificaelse sql_ins = "INSERT INTO tb_immobile (`IdServizio`, `CodiceAppartamento`, `Nome`, `IdLocalita`, `Localita`, `NumeroPiano`, `Piano`, `NumeroScalini`, `Camere`, `Singole`, `Matrimoniali`, `Bagni`, `Vani`, `IdTipo`, `IdPosizione`, `IdAspetto`, `IdRistrutturato`, `IdAmmobiliato`, `IdStato`, `Mq`, `Annesso`, `IdAnnessoRistrutturato`, `Giardino`, `Terrazza`, `Terreno`, `Cantina`, `AriaCondizionata`, `Ascensore`, `PostiAuto`, `Piscina`, `Tennis`, `IdRiscaldamento`, `Condominio`, `idAllegato`, `idUtente`, `idImportazione`, `idZona`, `idDove`, `homePage`, `codTipoVisaulizzazione`) VALUES "sql_ins = sql_ins&"(1,"&imm_codice&","&imm_nome&","&imm_provincia&",'"&imm_localita&"',"&imm_npiani&","&imm_piano&","&imm_scalini&","&imm_camere&","&imm_camere_sing&","&imm_camere_mat&","&imm_bagni&","&imm_vani&","&imm_tipo&","&imm_posizione&","&imm_aspetto&","&imm_ristrutturato&","&imm_ammobiliato&","&imm_stato&","&imm_mq&"... )"end if\[/code\]in the first for each i create and populate the variables, but some of them should be empty.