Unable to create a constant value of type 'System.Char' : <p>I'm getting the following error trying to group and sum some values via LINQ in EF6:</p>

<blockquote>
  <p>Unable to create a constant value of type 'System.Char'. Only primitive types or enumeration types are supported in this context.</p>
</blockquote>

<p>I've looked at half a dozen similar questions on StackOverflow and can't find my issue.  Here's the query:</p>

<pre><code>var q = from c in _context.HoursProviderCosts
        where c.PatientInsuranceCompanyName == insuranceName
            &amp;&amp; c.HoursDate &gt;= startDate
            &amp;&amp; c.HoursDate &lt;= endDate
        group c by new { c.ID, c.PatientFirstName, c.PatientLastName } into g
        select new Models.InsuranceCostListItem
        {
            PatientID = g.Key.ID,
            PatientName = g.Key.PatientFirstName + ' ' + g.Key.PatientLastName,
            Total = g.Sum(x =&gt; x.ProviderRate)
        };

return q.ToList();
</code></pre>

<p>Is it something in my grouping (which I'm new to)?  The underlying EF6 model is fine (I can expand the results view of <code>_context.HoursProviderCosts</code> and look at the data just fine).</p>

<p>Thanks</p>

<p>Edit: method signature:</p>

<pre><code>public List&lt;Models.InsuranceCostListItem&gt; InsuranceCostsListItems(DateTime periodStart, string insuranceName) {
</code></pre>
