title: npgsql : Selecting a null data throws exception with error "Column is Null"
body: <p>I am running npgsql v3.7 with .NetCore on Ubuntu.</p>
  
  <p>When I execute a select query and a cell in any row in the results is null, an exception is thrown with the error message "Column is null".</p>
  
  <p>I am having to work around this by putting every column in the select clause inside a case statement which tests for NULL</p>
  
  <pre><code>"CASE WHEN " + fieldName + " IS NULL THEN '' ELSE " + fieldName + " END "
  </code></pre>
  
  <p>This seems a bit extreme and should not be necessary.  Has anyone else come across this.</p>
  
  <p>Thanks.</p>