get listbox items method returns null value

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C#3.0

C#

I wrote the following method to get CheckedListBox Items and do some modifications, but it doesn't loop inside the

foreach (object o in lstKeyWordsForSearch.CheckedItems)

and return null value

public List<string> GetKeyWordsFormList()
{
    List<string> words = new List<string>();
    foreach (object o in lstKeyWordsForSearch.CheckedItems)
    {
        string s = o.ToString().ToLower();
        if (s != null)
        {
            string[] separated = s.Split(',');
            string[] arrremove = null;
            frmStopWordList stopWords = new frmStopWordList();
            arrremove = stopWords.getStopWords();
            for (int i = 0; i < separated.Length; i++)
            {
                for (int j = 0; j < arrremove.Length; j++)
                {
                    if (separated[i] == arrremove[j])
                    {
                        separated[i] = "";
                    }
                }
            } // remove stop words
            foreach (string word in separated)
            {
                if (!string.IsNullOrEmpty(word))
                {
                    if (!words.Contains(word))
                    {
                        words.Add(word);
                    }
                }
            }
        }
    }
    return words;
}</string></string></string>

where lstKeyWordsForSearch declared as name of CheckedListBox and I am getting that return value from another windows Form like following:

frmMainForm mainForm = new frmMainForm();
List<string> SearchKeyWords = mainForm.GetKeyWordsFormList();
foreach (string item in SearchKeyWords)
{
    MessageBox.Show(item);
}</string>

but MessageBox.Show(item); doesn't show anything when I call that public List<string> GetKeyWordsFormList()</string> method in the same form it gives output but when I call from another form it gives nothing.