title: Keep getting "Unexpected end of JSON input" when calling spreadsheets.values.batchUpdate
body: <p>I'm running this JS on a hosted service which wraps APIs in nodeJS libs, but I think it's pretty transparent:</p>
  
  <pre><code>var a=[{
     range: 'A1',
     values: [['Total issues',issues.length,'Last updated',new Date()]]
   },{
     range: 'A2',
     values: [['Number','Title','State']]
   }]
  for(let x=0;x&lt;issues.length;++x) {
    let i = issues[x];
    let id = i.number;
    a[a.length] = {
     range: 'A'+ (issues.length+1),
     values: [[i.number,i.title,i.state]]
   }
  }
  
  await google_sheets.spreadsheets.values.batchUpdate({
    spreadsheetId: input.sheet_id,
    body : { 
      data : a,
      valueInputOption: 'USER_ENTERED'
    }
  }, context);
  </code></pre>
  
  <p>When I run this the target sheet gets the first two rows updated with the static text, but nothing else (<code>issues</code> is result of calling GitHub API and works fine) - and I get the error in the title.</p>
  
  <p>When I called <code>update</code> for each issue instead of <code>batchUpdate</code> it worked but was slow and ran into API call limits.</p>
  
  <p>I think I even had one case where the sheet <em>was</em> properly updated but I still got the error.</p>
  
  <p>I've yet to figure out how to see the JSON emitted from this 3rd-party service, can anyone see an error in my code, or tell me if I can retrieve the JSON Google received?</p>