removeAttribute Javascript

Question

I am learning Javascript and have made the following function:

var marcaAgua = document.getElementById('marca-agua');

var reso = window.matchMedia("(min-width: 768px)");

function pngReso(reso){
  if (reso.matches){
     marcaAgua.removeAttribute("hidden");
     window.onscroll = function() {navbarFunc()};
  } else {
     console.log('entoru mobile');
     window.onscroll = null;
  }
}

pngReso(reso);
reso.addListener(pngReso);

However, in the browser keeps giving the error:

Cannot read Property 'removeAttribute' of null at pngReso

And the function isn’t executed, and I don’t know what I’m doing wrong.