Mono compiler says "The variable `myStream' is assigned but its value is never used"

gistfile1.cs

private void toolStripButtonChooseText_Click(object sender, EventArgs e)
        {
            Stream myStream = null;
            OpenFileDialog openFileDialog = new OpenFileDialog();

            openFileDialog.InitialDirectory = ".";
            openFileDialog.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
            openFileDialog.FilterIndex = 1;
            openFileDialog.RestoreDirectory = false;

            if (openFileDialog.ShowDialog() == DialogResult.OK)
            {
                Stop();

                try
                {
                    if ((myStream = openFileDialog.OpenFile()) != null)
                    {
                        _settings.TextFile = openFileDialog.FileName;
                        CurrentTextFile = _settings.TextFile;
                    }

                }
                catch (Exception ex)
                {
                    MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message);
                }
            }
        }