title: Google BigQuery, I lost null row when using 'unnest' function
body: <pre><code>#StandardSQL
  WITH tableA AS (
  SELECT ["T001", "T002", "T003"] AS T_id, [1, 5] AS L_id
  UNION ALL
  SELECT ["T008", "T009"] AS T_id, NULL AS L_id
  )
  
  SELECT * FROM tableA, UNNEST(L_id) AS unnest
  </code></pre>
  
  <p>When I executed this code, I expected the result such as that below.</p>
  
  <pre><code>RowNumber  T-id            L-id  unnest
  1          T001,T002,T003  1,5   1
  2          T001,T002,T003  1,5   5
  3          T004,T005       NULL  NULL
  </code></pre>
  
  <p>But I get this result instead:</p>
  
  <pre><code>RowNumber  T-id            L-id  unnest
  1          T001,T002,T003  1,5   1
  2          T001,T002,T003  1,5   5
  </code></pre>
  
  <p>I lost the third row.
  Then, I saw the official Google documentation, which states the following:</p>
  
  <pre><code>UNNEST treats NULL as follows.
   ・NULL and empty ARRAY generate zero rows.
   ・An ARRAY containing NULL generates a row containing a NULL value.
  </code></pre>
  
  <p>But I don't want to lose my null row.</p>
  
  <p>How can I keep the null row?</p>
  
  <p>Please tell me the solution...</p>