Coefficients (coeffs) in MATLAB for 0 coefficients of x^n

Question

syms x;
f = 6*x^6 - 25*x^5 + 31*x^4 - 31*x^2 + 25*x - 6;
cf = coeffs(f);
disp(cf);

for these peice of line I'm getting this as an output
[-6, 25, -31, 31, -25, 6]

But why I'm not getting 0 as coefficients of x^3,
while computing the roots of the from coefficients I need to have 0 as coefficients of x^3

output: [-6, 25, -31, 31, -25, 6]

my expectations: [-6, 25, -31, 0, 31, -25, 6]