Cannot read properties of null (reading 'classList')

JS только учусь и поэтому иногда вообще не понимаю что происходит.. Помогите понять где и как исправлять ошибку, пожалуйста. Ошибки таковы

Uncaught TypeError: Cannot read properties of null (reading 'classList')
    at FormValidator._toggleSaveButton (FormValidator.js:11:30)
    at FormValidator._trackEventListener (FormValidator.js:40:10)
    at FormValidator.enableValidation (FormValidator.js:50:10)
    at index.js:172:15
    at NodeList.forEach (<anonymous>)
    at enableValidation (index.js:162:12)
    at index.js:175:1

Код

FormValidator.js

export class FormValidator {
  constructor(formElement, enableValidationConfig) {
    this._formElement = formElement;
    this._enableValidationConfig = enableValidationConfig;
    this._inputList = Array.from(this._formElement.querySelectorAll(this._enableValidationConfig.inputSelector));
    this._submitSaveButton = this._formElement.querySelector(this._enableValidationConfig.submitButtonSelector);
  }
 
  _toggleSaveButton() {
    if (this._formElement) {
      this._submitSaveButton.classList.remove(this._enableValidationConfig.inactiveButtonClass); //config
      this._submitSaveButton.disabled = false;
    } else {
      this._submitSaveButton.classList.add(this._enableValidationConfig.inactiveButtonClass); //config
      this._submitSaveButton.disabled = true;
    }
  }

  _showInputError(inputElement) {
    const errorElement = this._formElement.querySelector(`.popup__input-error_type_${inputElement.name}`);
    inputElement.classList.add(this._enableValidationConfig.inputErrorClass);
    errorElement.textContent = validationMessage;
  };

  _hideInputError(inputElement) {
    const errorElement = this._formElement.querySelector(`.popup__input-error_type_${inputElement.name}`);
    inputElement.classList.remove(this._enableValidationConfig.inputErrorClass);
    errorElement.textContent = '';
  };

  _isValid(inputElement) {
    if (!inputElement.validity.valid) {
      this._showInputError(inputElement);
    } else {
      this._hideInputError(inputElement);
    }
  };

  _trackEventListener() {
    this._toggleSaveButton();
    this._inputPopup.forEach((inputElement) => { // inputPopup
      inputElement.addEventListener("input", () => {
        this._isValid(inputElement);
        this._toggleSaveButton();
      });
    });
  }

  enableValidation() {
    this._trackEventListener();
  }
}

index.js

import { FormValidator } from "../scripts/FormValidator.js";
import { Card } from "../scripts/Card.js";

// 0.1 общее
const closeButtons = document.querySelectorAll('.popup__close');
// 0.1 общее

// 1.1 окно редактирования профиля
const profilePopup = document.querySelector('.profile-popup');
const buttonEditProfileOpen = document.querySelector('.profile__editbutton');
const getName = document.querySelector('.profile__name');
const getAbout = document.querySelector('.profile__about');
const editForm = document.querySelector('.popup__container');
const nameInput = editForm.querySelector('.popup__input_type_name');
const aboutInput = editForm.querySelector('.popup__input_type_about');
//const buttonEditProfileSave = document.querySelector('.popup__savebutton');
//const buttonEditProfileClose = document.querySelector('.popup__closebutton');
//const profileEditForm = document.querySelector('.popup__editprofile');
// 1.1 окно редактирования профиля

// 2.1 окно добавления фотокарточки
//const popupPhoto = document.querySelector('.popup-addphoto');
const buttonAddPhotoOpen = document.querySelector('.profile__addbutton');
//const editFormPhoto = document.querySelector('.popup__container-addphoto');
//const buttonAddPhotoSave = document.querySelector('.popup__savebutton-addphoto');
//const buttonAddPhotoClose = document.querySelector('.popup__closebutton-addphoto');
// 2.1 окно добавления фотокарточки 

// 3.1 карточки 
const elementsAlbum = document.querySelector('.album__elements');
const albumSection = document.querySelector('.popup-openphoto');
const albumPhoto = albumSection.querySelector('.popup__photo-openphoto');
const albumElementsInfo = albumSection.querySelector('.popup__photo-info');
//const buttonElementsAlbumClose = albumSection.querySelector('.popup__closebutton-photo');
const popupAddphoto = document.querySelector('.popup-addphoto');
const editFormAddPhoto = popupAddphoto.querySelector('.popup__editprofile-addphoto');
const titleInput = popupAddphoto.querySelector('.popup__input-addphoto_type_title');
const linkInput = popupAddphoto.querySelector('.popup__input-addphoto_type_link');
//const elementPhoto = document.querySelector('.element__photo');
const templateElement = document.querySelector('#template-element').content;
const initialCards = [
  {
    name: 'NY, caladium',
    link: 'https://images.unsplash.com/photo-1596670616944-60db8c2a24f5?ixlib=rb-4.0.3&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=464&q=80'
  },
  {
    name: 'Altai Republic, dahlia',
    link: 'https://images.unsplash.com/photo-1631100615885-16e05606aa11?ixlib=rb-4.0.3&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=435&q=80'
  },
  {
    name: 'Earth, Java Script',
    link: 'https://i.gifer.com/8Ggv.gif'
  },
  {
    name: 'Sri-Lanka, alocasia',
    link: 'https://images.unsplash.com/photo-1547070078-442aa97f595a?ixlib=rb-4.0.3&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=1170&q=80'
  },
  {
    name: 'Vietnam, nymphaea',
    link: 'https://images.unsplash.com/photo-1560741232-886afab774be?ixlib=rb-4.0.3&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=327&q=80'
  },
  {
    name: 'Detroit, papaver',
    link: 'https://images.unsplash.com/photo-1589720061712-10b534c7218e?ixlib=rb-4.0.3&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=435&q=80'
  }
];
// 3.1 карточки

// 4.1
const enableValidationConfig = {
  formSelector: '.popup__editprofile',
  inputSelector: '.popup__input',
  submitButtonSelector: '.popup__savebutton',
  inactiveButtonClass: 'popup__savebutton_error',
  inputErrorClass: 'popup__input-errorline',
};
// 4.1

// 0.2 общее
function handlePressEsc(event) {
  if (event.key === "Escape") {
    const openedPopupActive = document.querySelector(".popup_opened");
    closePopup(openedPopupActive);
  }
}

function handleClickOverlay(event) {
  if (event.target.classList.contains("popup")) {
    closePopup(event.target);
  }
}

function openPopup(popup) {
  popup.classList.add('popup_opened');
  document.addEventListener("keyup", handlePressEsc);
  document.addEventListener("click", handleClickOverlay);
}

function closePopup(popup) {
  popup.classList.remove('popup_opened');
  document.removeEventListener("keyup", handlePressEsc);
  document.removeEventListener("click", handleClickOverlay);
}

closeButtons.forEach((button) => {
  const popup = button.closest('.popup');
  button.addEventListener('click', () => closePopup(popup));
});
// 0.2 общее

//1.2 окно редактирования профиля
// function openProfilePopup() {
//   nameInput.value = getName.textContent;
//   aboutInput.value = getAbout.textContent;
//   closePopup(profilePopup);
// }

function handleProfileFormSubmit(evt) {
  evt.preventDefault();
  getName.textContent = `${nameInput.value}`;
  getAbout.textContent = `${aboutInput.value}`;
  closePopup(profilePopup);
  formValidator["editForm"].resetValidation();
}
// 1.2 окно редактирования профиля

// 3.2 карточки 
function openPhoto(link, alt) {
  albumPhoto.src = link;
  albumPhoto.alt = alt;
  albumElementsInfo.textContent = alt;
  openPopup(albumSection);
}

function createCard(item) {
  const cardElement = new Card(item, templateElement, openPhoto).createNewCard();
  return cardElement
}

function createAddCard(evt) {
  evt.preventDefault();
  const newElement = createCard({ name: titleInput.value, link: linkInput.value });
  elementsAlbum.prepend(newElement);
  closePopup(popupAddphoto);
  editFormAddPhoto.reset();
  formValidator["editFormAddPhoto"].resetValidation();
  //toggleSaveButton(buttonAddPhotoSave, false, enableValidationConfig);
}

function renderInitialCards() {
  const expandPhoto = initialCards.map(createCard);
  elementsAlbum.append(...expandPhoto);
}
renderInitialCards();
// 3.2 карточки

// 4.2
const formValidator = {}; 

function enableValidation() {
  const editForm = document.querySelectorAll(enableValidationConfig.formSelector);
  editForm.forEach((formElement, enableValidationConfig) => {
    //trackEventListener(formElement, enableValidationConfig);
    formElement.addEventListener("submit", (evt) => {
      evt.preventDefault();
    });
    const submitSaveButton = formElement.querySelector(enableValidationConfig.submitButtonSelector);
    //toggleSaveButton(submitSaveButton, formElement.checkValidity(), enableValidationConfig);
    const validator = new FormValidator(formElement, enableValidationConfig);
    const formName = formElement.getAttribute("name");
    formValidator[formElement] = validator;
    validator.enableValidation();
  });
}
enableValidation();
// 4.2

// 1.3 окно редактирования профиля
buttonEditProfileOpen.addEventListener('click', () => {
  nameInput.value = getName.textContent;
  aboutInput.value = getAbout.textContent;
  openPopup(profilePopup)
});
editForm.addEventListener('submit', handleProfileFormSubmit);
// 1.3 окно редактирования профиля

// 2.3 окно добавления фотокарточки
buttonAddPhotoOpen.addEventListener('click', () => openPopup(popupAddphoto));
// 2.3 окно добавления фотокарточки

// 3.3 карточки
editFormAddPhoto.addEventListener('submit', createAddCard);
// 3.3 карточки