title: NULL value shown on filter regardless
body: <p>I have created a calculated field to only show week numbers for the latest four weeks from today. I called it <em>latest_4_weeks</em> with the following definition:</p>
  
  <pre><code>if (([week_number] &lt;= datepart('week',today())) and ([week_number] &gt; datepart('week',today()) -4)) then [week_number]
  end
  </code></pre>
  
  <p>When I add this field to my columns an unwanted <code>NULL</code> value shows up. I still haven't been able to tell the Tableau to ignore all the null values using <code>IFNULL()</code>, etc.</p>
  
  <p>And when I manually filter out the <code>NULL</code> value, the filter no longer works as it should. Since it will now apply the current values and all other values that relate to next week will be ignored.</p>
  
  <p><a href="https://i.stack.imgur.com/QTj9r.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QTj9r.png" alt="enter image description here"></a></p>
  
  <p>How can I effectively remove <code>NULL</code> in my calculated field?</p>