Julia ERROR: 'Can't Promote to Common Type' for multivariate polynomials in Nemo Library

Question

I am new to Julia and have been trying to compute some polynomials using the Nemo library's multivariate polynomials. I have the following code:

    R = GF(2); # create finite field
    S, (z, x) = PolynomialRing(R, ["z", "x"]); # Multivariate polynomial

    # polynomial initialisations
    L = x^0; 
    E_L = x^0;
    E = x*0;
    
    a = z;
    w = [1 1 a^3 a^2 a^1 0 0];
    
    n = length(w); #input vector, in terms of a
    j = 1;
    for i = 1:n

        if(w[i] != 0)

            L = L*(1-(a^i)*x); # equation for the locator polynomial
            
            if(i != j)
                E_L = E_L*(1-(a^j)*x);
            end
            j = j + 1;

            E = E + w[i]*(a^i)*E_L; # LINE WITH ERROR 

        end
    end

I am not entirely sure why the line with the expression for E throws an error.

I have tried a similar thing with the declaration for L: L = L + L*(1-(a^i)*x) to see whether it was something to do with the addition of two polynomials, however, this works fine. Therefore, I am confused as to why E's expression throws an error.

Any help would greatly appreciated! Thanks in advance!