title: Error inserting nullable integers into bigquery using python API
body: <p>I am trying to use the bigquery python API to insert data into bigquery tables. More specifically the command:</p>
  
  <pre><code>errors = client.insert_rows(table, rows[i*BATCH_SIZE:])
  </code></pre>
  
  <p>The column <strong>gas_used</strong> in my table has a datatype INTEGER and is NULLABLE. But I get the following error while inserting rows with null values in <strong>gas_used</strong>.</p>
  
  <blockquote>
    <p>[{'index': 0, 'errors': [{u'debugInfo': u'', u'reason': u'invalid',  u'message': u'Cannot convert value  to integer (bad value):', u'location': u'gas_used'}]}]</p>
  </blockquote>
  
  <p>Here, is the schema of my table:</p>
  
  <pre><code>block_number,transaction_hash,type,trace_address,subtraces,transaction_position,from,to,value_wei,start_gas,input,gas_used,contract_address,output,error
  </code></pre>
  
  <p>and, here is the row which throws the error:</p>
  
  <pre><code>[('5000001', '0x2cfd7194877466e6adb87222e5876c4babf8bd59de299698fdce7f0a9a232932', 'call', '[]', '0', '11', '0x77cb68e788aa79640b8a613431cdb10d83208d47', '0x4b3ee0ac445d954f8bca68f9538d54e9633890f6', '349950000000000', '0', '0x', '', '', '', 'Out of gas')]
  </code></pre>
  
  <p><strong>gas_used</strong> column is the fourth last column in the schema.</p>