title: COUNTing IS NULL returns 0 or with an Error [BigQuery]
body: <p>I want to find the number of data that is NULL but i do not know why this code returns an error: (Error Message said there was a problem with my WHERE)</p>
  <pre><code>SELECT first_review, COUNT (1) AS firstreviewisnull
  FROM [table_name]
  GROUP BY first_review
  WHERE first_review IS NULL
  </code></pre>
  <p>I tried this code and the count returns to 0 - which I know is incorrect:</p>
  <pre><code>SELECT COUNT(first_review) AS firstreviewisnull
  FROM [table_name]
  WHERE first_review IS NULL
  </code></pre>
  <p>If possible, please help to:</p>
  <ul>
  <li>explain what i did wrong</li>
  <li>provide with the correct code</li>
  </ul>
  <p>thank you!</p>