metoda includes is not a function

Nie wiem czemu mam taki komunikat, wpisuje np. w input brr - czyli coś czego nie ma w ul i wtedy dochodzę do drugiego ifa i jest ten komunikat, oto kod

html

<form action="">
    <input id='search' type="text">
    <button>Dodaj zadanie</button>
   </form>
   <h1>Liczba zadań: <span>0</span></h1>
   <ul>
    <li>brukselka</li>
    <li>groch</li>
    <li>batat</li>
    <li>ziemniak</li>
    <li>burak</li>
    <li>fasola</li>
    <li>marchewka</li>
    <li>pietruszka</li>
    <li>por</li>
    <li>cebula</li>
   </ul>

js

const form = document.querySelector('form');
const inputSearch = document.getElementById('search');
const ul = document.querySelector('ul');
const liElements = document.querySelectorAll('li');
const taskNumber = document.querySelector('h1 span');

   const addTask = (e) => {
    e.preventDefault()
    const titleTask = inputSearch.value;
    if (titleTask === "") return;
    const task = document.createElement('li');
    task.innerHTML = titleTask + "<button>Usuń</button>";
   
    ul.appendChild(task);
    input.value = "";
   }
const searchTask = (e) => {
 const searchText = e.target.value;
 let letter = searchText[0];
 let tasks = [...liElements];
 const first = tasks[0];
 tasks = tasks.filter(li => li.textContent.includes(searchText))
 console.log(tasks.forEach(li => ul.appendChild(li)))
 if (tasks.length == 0) {
    if (first.includes(letter)) {
       console.log('brak');
    }
 }
}
form.addEventListener('submit', addTask);
inputSearch.addEventListener('input', searchTask)

first.textContent.includes(letter) ?