title: IN clause in SOQL not working as expected
body: <p>Code snippet1:</p>
  
  <pre><code>list&lt;string&gt; abc = new list&lt;string&gt;{'a1V44000008TyEEEA0'};  
  list&lt;task&gt; t = [ SELECT Id FROM Task WHERE (whatId in :abc or Whoid in :abc)]
  system.debug('--&gt;'+t.size());
  </code></pre>
  
  <p>Above code segment is working as expected. </p>
  
  <p>Code snippet2:</p>
  
  <pre><code>list&lt;string&gt; abc = new list&lt;string&gt;{null, 'a1V44000008TyEEEA0'};  
  list&lt;task&gt; t = [ SELECT Id FROM Task WHERE (whatId in :abc or Whoid in :abc)]
  system.debug('--&gt;'+t.size());
  </code></pre>
  
  <p>Snippet2 is returning a result as if there is no WHERE clause. 
  What is the logic behind this or is it any bug?</p>