title: Execute LINQ with or without where clause
body: <p>In my example i want to get promotion elements for a promo code name that is provided if name is not provided then take all available promotions.</p>
  
  <pre><code>var result = from row in promoCodes.AsEnumerable() 
               where  (
                   !String.IsNullOrEmpty(fieldTitle) &amp;&amp; 
                   !String.IsNullOrEmpty(filterValue) &amp;&amp; 
                   row[fieldTitle].Equals(filterValue)
               ) || true
               select new PromoCodeInfoContainer
               {
                   BannerLink = row["BannerLink"] as string
                   ....
               };
  </code></pre>
  
  <p>I tried to follow SQL technique where if no conditions provided then OR will be whatever that doesn't impact selection (|| true). In linq this didn't work, it always returns all entries regardless of "fieldTitle" and "filterValue" are not empty. Can anybody suggest a right way to do it?</p>