title: SQL query returns nothing when looking for records that are not in another table
body: <p>I have created two tables and populated them:</p>
  <pre><code>CREATE TABLE FirstTab (
            id integer, 
            name VARCHAR(10) );
       
  INSERT INTO FirstTab VALUES (5,'Pawan'), (6,'Sharlee'), (7,'Krish'),
       (NULL,'Avtaar');
       
  CREATE TABLE SecondTab (
           id integer  );
      
  INSERT INTO SecondTab VALUES (5), (NULL);
  </code></pre>
  <p>I am trying to find the records from FirstTab that are not in SecondTab (I guess like a custom outer join?)</p>
  <p>But this query returns nothing:</p>
  <pre><code>SELECT * FROM FirstTab AS ft WHERE ft.id NOT IN ( SELECT id FROM SecondTab );
  </code></pre>
  <p>What is wrong with it? I should get 2 records, not 0.</p>
  <p>I'm using Postgres on PgAdmin 4</p>