title: How to query an Entity Framework entity for null field value with DotConnect for PostgreSQL
body: <p>I observe a strange behavior when querying for null field an Entity Framework entity with the Devart DotConnect for PostgreSQL connector.</p>
  
  <p>For example: If I made the 2 following tests:</p>
  
  <pre>
  var test1 = context.blocs.Where(x => x.id_bloc == null);
  
  var test2 = context.blocs.Where(x => x.id_bloc == 100);
  </pre>
  
  <p>When checking for EF auto-generated SQL query I obtain the following results:</p>
  
  <p>Result for test1:</p>
  
  <pre>
  {SELECT 
   CAST(NULL AS int) AS "C1",
   CAST(NULL AS varchar) AS "C2",
   CAST(NULL AS varchar) AS "C3",
   CAST(NULL AS varchar) AS "C4"
  FROM  ( SELECT 1 AS X) AS "SingleRowTable1"
  WHERE true = false}
  </pre>
  
  <p>Result for test2:</p>
  
  <pre>
  {SELECT 
  "Extent1".id_bloc,
  "Extent1".numero,
  "Extent1".nom,
  "Extent1".titre
  FROM "role".bloc AS "Extent1"
  WHERE "Extent1".id_bloc = 100}
  </pre>
  
  <p>The result when querying for null field is very strange... I was expecting a result similar to the test 2 result but with an <code>"Extent1".id_bloc IS NULL</code> WHERE clause...</p>
  
  <p>Is it a bug? How can I effectively query for null field?</p>