I have a control that, upon postback, saves form results back to the database. It populates the values to be saved by iterating through the querystring. So, for the following SQL statement (vastly simplified for the sake of discussion)...

```
UPDATE MyTable
SET MyVal1 = @val1,
    MyVal2 = @val2
WHERE @id = @id

```

...it would cycle through the querystring keys thusly:

```
For Each Key As String In Request.QueryString.Keys
    Command.Parameters.AddWithValue("@" & Key, Request.QueryString(Key))
Next

```

HOWEVER, I'm now running into a situation where, under certain circumstances, some of these variables may not be present in the querystring. If I don't pass along val2 in the querystring, I get an error: `System.Data.SqlClient.SqlException: Must declare the scalar value "@val2"`.

Attempts to detect the missing value in the SQL statement...

```
IF @val2 IS NOT NULL
UPDATE MyTable
SET MyVal1 = @val1,
    MyVal2 = @val2
WHERE @id = @id

```

... have failed.

What's the best way to attack this? Must I parse the SQL block with RegEx, scanning for variable names not present in the querystring? Or, is there a more elegant way to approach?

UPDATE: Detecting null values in the VB codebehind defeats the purpose of decoupling the code from its context. I'd rather not litter my function with conditions for every conceivable variable that might be passed, or not passed.