title: LINQ - exclude the filter when the value is NULL
body: <p>I am trying to see if there is any better way of writing the query below when there is an optional parameter (CountryId) which can be NULL</p>
  
  <pre><code> public static IEnumerable&lt;Game&gt; GameByMatchingName(this IRepositoryAsync&lt;Game&gt; repository,  string searchCriteria, string countryId = null)
          {
              return repository
                  .Queryable()
                  .Where(x =&gt; (countryId != null ? x.CountryId == countryId : true) &amp;&amp; x.Name.Contains(searchCriteria))
                  .AsEnumerable();
          }
  </code></pre>
  
  <p>Ideally , I would like to exclude the criteria in the filter when CountryId is NULL.</p>
  
  <p>-Alan-</p>