title: Grouping datatable causing null reference exception in LINQ
body: <p>Hi i have a query which run with no problem</p>
  
  <pre><code> var v = (from r in cTable.AsEnumerable()
           group r by r.Field&lt;string&gt;("Name") into g
           select new
           {
              CallType = g.Key,
              Count = g.Count()
           });        
  </code></pre>
  
  <p>This runs quite good. But when i make change by adding</p>
  
  <pre><code> var v = (from r in cTable.AsEnumerable()
           group r by r.Field&lt;string&gt;("Name").Replace(",", "") into g
           select new
           {
              CallType = g.Key,
              Count = g.Count()
           });              
  </code></pre>
  
  <p>It gives me <code>Object Refrenence not set to instance errror</code> Why so ? I just wanna any comma in name column should be avoid in grouping the data i.e 'Rajeev' and Ra,jeev' should be count as 'Rajeev' while grouping</p>