I got this parameter:

```
$objDbCmd.Parameters.Add("@telephone", [System.Data.SqlDbType]::VarChar, 18) | Out-Null;
$objDbCmd.Parameters["@telephone"].Value = $objUser.Telephone;

```

Where the string `$objUser.Telephone` can be empty. If it's empty, how can I convert it to `[DBNull]::Value`?

I tried:

```
if ([string]:IsNullOrEmpty($objUser.Telephone)) { $objUser.Telephone = [DBNull]::Value };

```

But that gives me the error:

> 
> Exception calling "ExecuteNonQuery" with "0" argument(s): "Failed to convert parameter value from a ResultPropertyValueCollection to a String."
> 
> 
> 

And if I convert it to a string, it inserts an empty string `""`, and not `DBNull`.

How can this be accomplished?

Thanks.