title: Showing an empty cell when data is null with DefaultCellStyle.Format set
body: <p>I have a datagridview.  The dgv's data source is a 'ReadOnlyCollection' of objects.  One of the properties of the object in the 'ReadOnlyCollection' is a nullable 'DateTime'.  What I'm trying to do is show a blank cell where the 'DateTime' is null, but apply a different format to the DateTime column, by doing:</p>
  
  <pre><code>TimeOutColumn.DefaultCellStyle.Format = "MM/dd/yyyy HH:mm";
  </code></pre>
  
  <p>The only problem is that sets all of my null entries to the DateTime.Min value.  </p>
  
  <p>'history' is the ReadOnlyCollection.
  Here's the current code:</p>
  
  <pre><code>'DataGridViewTextBoxColumn TimeOutColumn = new DataGridViewTextBoxColumn();
              TimeOutColumn.DataPropertyName = "timeout";
              TimeOutColumn.HeaderText = "Time Out";                
  
              ddgGHistory.Columns.Add(BadgeTypeIDColumn);
              ddgGHistory.Columns.Add(EmployeeColumn);
              ddgGHistory.Columns.Add(TimeInColumn);
              ddgGHistory.Columns.Add(TimeOutColumn);
  
              ddgGHistory.DataSource = history
  
              ddgGHistory.Columns[3].DefaultCellStyle.Format = "MM/dd/yyyy HH:mm";
              ddgGHistory.Columns[3].DefaultCellStyle.NullValue = "";
  </code></pre>