C# Exception Handling continue on error

Question

I have a basic C# console application that reads a text file (CSV format) line by line and puts the data into a HashTable. The first CSV item in the line is the key (id num) and the rest of the line is the value. However I've discovered that my import file has a few duplicate keys that it shouldn't have. When I try to import the file the application errors out because you can't have duplicate keys in a HashTable. I want my program to be able to handle this error though. When I run into a duplicate key I would like to put that key into a arraylist and continue importing the rest of the data into the hashtable. How can I do this in C#

Here is my code:

---

private static Hashtable importFile(Hashtable myHashtable, String myFileName) {

        StreamReader sr = new StreamReader(myFileName);
        CSVReader csvReader = new CSVReader();
        ArrayList tempArray = new ArrayList();
        int count = 0;

        while (!sr.EndOfStream)
        {
            String temp = sr.ReadLine();
            if (temp.StartsWith(" "))
            {
                ServMissing.Add(temp);
            }
            else
            {
                tempArray = csvReader.CSVParser(temp);
                Boolean first = true;
                String key = "";
                String value = "";

                foreach (String x in tempArray)
                {
                    if (first)
                    {
                        key = x;
                        first = false;
                    }
                    else
                    {
                        value += x + ",";
                    }
                }
                myHashtable.Add(key, value);
            }
            count++;
        }

        Console.WriteLine("Import Count: " + count);
        return myHashtable;
    }

Answer 1

if (myHashtable.ContainsKey(key))
    duplicates.Add(key);
else
    myHashtable.Add(key, value);