Uncaught TypeError: Cannot read property 'checked' of null

function CheckTest() { 
  var qCounts = parseInt(document.getElementById('sQuestionsCount').innerHTML); 
  var maxScore = parseFloat(document.getElementById('sMaxPoints').innerHTML); 
  var curScore = 0; 
  for (var i = 1; i <= qCounts; i++) { 
    var ansCounts = document.getElementById('dqres' + i).getAttribute('answerscount'); 
    var scoringType = document.getElementById('dqres' + i).getAttribute('scoringtype'); 
    var answertype = document.getElementById('dqres' + i).getAttribute('answertype'); 
    var iFilled = false; 
    for (var j = 1; j <= ansCounts; j++) { 
      var input = document.getElementById('ans' + i + "-" + j); 
      if (answertype == "10") { 
        if (input.checked) { 
          iFilled = true; 
          if (scoringType == "0") curScore = curScore + parseInt(input.getAttribute("score")); 
        } 
      }

<input id="bntcheck" type="button" onclick="CheckTest(" ");" value="Перевірити" class="otp-test-checkresult-btn"></input> 
<div id="dResults" class="otp-test-results"> 
  <span class="otp-test-results-header">Ваш результат:</span> 
  <div class="otp-test-results-vals"> 
    <span class="otp-test-results-text">Кількість балів:</span> 
    <span id="sScore" class="otp-test-results-value"></span><br /> 
    <span class="otp-test-results-text">Відсоток рішення:</span> 
    <span id="sPercent" class="otp-test-results-value"></span><br /> 
    <span class="otp-test-results-text">Оцінка:</span> 
    <span id="ocenka" class="otp-test-results-value"></span> 
  </div>