string[] array is returning error of "Object reference not set to an instance of an object."

Question

Submitting a POST ajax call to a controller with an array parameter.

I have a parameter array,
I have a static array that a I use to check the parameter array against.
I have a third array created using the .Except method to create an array that is everything but the parameter values.

The POST ajax call works like it should. I can return and see the values I am sending to it. That's what I'm doing with that quick TempData. So, I know the parameter is not empty.

Here is the controller:

    [HttpPost]
    public ActionResult MyAction(string[] subLineNames)
    {
       //Static array to check against parameter
        string[] sublineArray = new string[] { "BI/PD", "Hired", "Non-Owned", "PIP", "Addtl-PIP", "Medical Payments", "UM PD", "UM CSL", "UIM CSL", "Terrorism" };

        //Create new array for all minus the values in the parameter
        /* The error happens here. The .Trim is causing some issue I can't see.  */
        /* I know that jquery ajax call is sending a bunch of white space, so I use trim to get rid of the white space characters. */
        string[] DifferArray = sublineArray.Except(subLineNames.Select(m => m.Trim())).ToArray();

        //Test to ensure the array parameter is not empty. (it works and brings back what I sent to it)
        if (subLineNames != null)
        {
            for (int i = 0; i < subLinesNames.Length - 1; i++)
            {
                TempData["AA"] += subLineNames[i];
            }
        }

    }

Frustrating because I had this working prior. I didn't change anything that would cause it to now do this. Any help would be so appreciated.

Does this answer your question? What is a NullReferenceException, and how do I fix it? — gunr2171
– gunr2171, Commented Nov 5, 2019 at 18:43
@swapmeet_Lou What are you trying to accomplish by your ajax? Are you trying to change the View? You're returning a string "Testing" from your controller. — Ryan Wilson
– Ryan Wilson, Commented Nov 5, 2019 at 18:43
On what line and which variable does it happen to? Probably subLineNames is null — the_lotus
– the_lotus, Commented Nov 5, 2019 at 18:46
@Ryan Wilson. I am submitting these values to a table i have set up. I left it out of the controller because that's not where to the problem is. Plus, if I can't get this to work in this simplistic manner, I can't insert them into the table. This was literally working a week ago and something I did caused this to screw up. I just can't see why. Even at this most basic level — swapmeet_Lou
– swapmeet_Lou, Commented Nov 5, 2019 at 18:48
If an element of subLineNames contains a null value, then you try to call .Trim() on it.. ker-pow. Without seeing the actual values there's no way to be certain. I'd set a breakpoint on this method and examine what was actually there.. then post that here so we can be of more help. Lastly, your action method doesn't return anything. — Sam Axe
– Sam Axe, Commented Nov 5, 2019 at 19:06

Tom Faltesek · Accepted Answer · 2019-11-05 19:17:14Z

3

Perhaps you need to null-check the elements in your parameter array before calling .Trim() on them:

string[] DifferArray = sublineArray.Except(subLineNames.Where(m => !string.IsNullOrWhiteSpace(m)).Select(m => m.Trim())).ToArray();

Better yet, you can store a reference to your sanitized parameter array:

[HttpPost]
public ActionResult MyAction(string[] subLineNames)
{
    if (subLineNames == null)
    {
        return new HttpStatusCodeResult(HttpStatusCode.BadRequest, $"You must provide {nameof(subLineNames)}.");
    }

    var sanitizedSubLineNames = subLineNames.Where(m => !string.IsNullOrWhiteSpace(m)).Select(m => m.Trim());
    var sublineArray = new string[] { "BI/PD", "Hired", "Non-Owned", "PIP", "Addtl-PIP", "Medical Payments", "UM PD", "UM CSL", "UIM CSL", "Terrorism" };
    var differArray = sublineArray.Except(sanitizedSubLineNames).ToArray();

    // Do something...
}

edited Nov 5, 2019 at 19:17

answered Nov 5, 2019 at 18:58

Tom Faltesek

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2 Comments

swapmeet_Lou Over a year ago

Thank you. the .Where(m => !string.IsNullOrWhiteSpace(m)) was what solved it for me. I was definitely wrong in my first NOT NULL assessment, but I can't for the life of me figure out how it happened and where I could have gone to find that answer to solve it. I was telling Sam above that I send checkbox values to the controller and checked to see what I was actually sending. I will dive deeper into the sanitized reference you gave as well. Thank you.

Tom Faltesek Over a year ago

Glad you figured out the issue. Cheers.

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