Error code Cannot read properties of null (reading 'appendChild)

Question

I'm trying to run my code for my To do list project but keep getting the error (cannot read appendChild).

let addToDoButton = document.getElementById('addToDo');
let toDoContianer = document.getElementById('toDoContianer');
let inputField = document.getElementById('inputField');

addToDoButton.addEventListener('click', function() {
  var paragraph = document.createElement('p');
  paragraph.classList.add('paragraph-styling');
  paragraph.innerText = inputField.value;
  toDoContianer.appendChild(paragraph);
  
  inputField.value = "";

  paragraph.addEventListener('click', function() {
    paragraph.style.textDecoration = 'line-through';
  });

  paragraph.addEventListener('dblClick', function() {
    toDoContianer.removeChild(paragraph);
  });
});