How do you test for null elements in System.Array

Question

I'm parsing an excel document into a System.Array and then using this data to develop a DataTable. The problem is that not every element in the System.Array contains a string and is null. See image below:

My question is how to I test for the null case.

Here is my method:

public static System.Data.DataTable ConvertCSVtoDataTable(string strFilePath)
    {
        System.Data.DataTable dt = new System.Data.DataTable();
        StreamReader sr = new StreamReader(strFilePath);
        string[] headers = sr.ReadLine().Split(',');
        foreach (string header in headers)
            dt.Columns.Add(header);
        sr.Close();

        Microsoft.Office.Interop.Excel.Workbook wb = null;
        Microsoft.Office.Interop.Excel.Worksheet ws = null;
        Microsoft.Office.Interop.Excel.Application app = null;
        int lastRow = 0;

        app = new Microsoft.Office.Interop.Excel.Application();
        app.Visible = false;
        wb = app.Workbooks.Open(strFilePath);
        ws = (Microsoft.Office.Interop.Excel.Worksheet)wb.Sheets[1];
        lastRow = ws.Cells.SpecialCells(Microsoft.Office.Interop.Excel.XlCellType.xlCellTypeLastCell).Row;
        int currentRow = 0;
        for (int index = 2; index <= lastRow; index++)
        {
            System.Array values = (System.Array)ws.get_Range("A" + index.ToString(), "M" + index.ToString()).Cells.Value;

                dt.Rows.Add();
            dt.Rows[currentRow]["Plugin ID"] = values.GetValue(1, 1).ToString();
            dt.Rows[currentRow]["CVE"] = values.GetValue(1, 2).ToString();
            dt.Rows[currentRow]["CVSS"] = values.GetValue(1, 3).ToString();
            dt.Rows[currentRow]["Risk"] = values.GetValue(1, 4).ToString();
            dt.Rows[currentRow]["Host"] = values.GetValue(1, 5).ToString();
            dt.Rows[currentRow]["Protocol"] = values.GetValue(1, 6).ToString();
            dt.Rows[currentRow]["Port"] = values.GetValue(1, 7).ToString();
            dt.Rows[currentRow]["Name"] = values.GetValue(1, 8).ToString();
            dt.Rows[currentRow]["Synopsis"] = values.GetValue(1, 9).ToString();
            dt.Rows[currentRow]["Description"] = values.GetValue(1, 10).ToString();
            dt.Rows[currentRow]["Solution"] = values.GetValue(1, 11).ToString();
            dt.Rows[currentRow]["See Also"] = values.GetValue(1, 12).ToString();
            dt.Rows[currentRow]["Plugin Output"] = values.GetValue(1, 13).ToString();
            currentRow++;
        }
        return dt;
    }

Here are some checks I've tried but didn't work

if (!values.Equals(null))
   dt.Rows[currentRow]["CVSS"] = values.GetValue(1, 3).ToString();
else
    dt.Rows[currentRow]["CVSS"] = "";

It appears this doesn't work because it seems like it is checking to see if any elements exist, not if the specfic element at this location is null.

if (values.GetValue(1, 3).ToString() == null)
    dt.Rows[currentRow]["CVSS"] = "";
else
   dt.Rows[currentRow]["CVSS"] = values.GetValue(1, 3).ToString();

This throws a NullReferenceExecption: Object reference not set to an instance of an object.

Answer 1

• The expression values.Equals(null) will throw on null, it won't return true.
• Calling anything.ToString() will also throw on null, it won't return a null (or empty) string reference.

What you want to do is probably just:

if(values.GetValue(1, 3) == null) ...

Answer 2

Change if (values.GetValue(1, 3).ToString() == null) to

if (values.GetValue(1, 3) == null)

---

Effectively your if, as you have written it could be "translated" to if(null.ToString() ...) in the case the value itself is null. And you can't call anything on null.

Answer 3

You could use the null conditional operator (?.) in conjunction with Null-Coalescing Operator (??) like this:

dt.Rows[currentRow]["CVSS"] = values.GetValue(1, 3)?.ToString() ?? "" 

With the null conditional operator (?.) GetValue(1,3) will be evaluated only if it not null. If it null dt.Rows[currentRow]["CVSS"] will have a string empty value ("").