Maximum Likelihood estimation of GJR - Offset estimate

I'm fitting GJR conditional variance model to time series of returns using Maximum Likelihood estimation. Is there a way to obtain ML estimate of series mean? Offset parameter doesn't appear in the estimates even when I specify initial value of Offset as a series mean (see code below).

Thank you!

Code:

mu = mean(y); Mdl = gjr(1, 1); [EstMdl, EstParamCov, logL, info] = estimate(Mdl, y(2:end), 'E0', y(1), 'Offset0', mu);

Output:

>> EstMdl

EstMdl =

    GJR(1,1) Conditional Variance Model:
    --------------------------------------  
    Distribution: Name = 'Gaussian'
               P: 1
               Q: 1
        Constant: 2e-07
           GARCH: {0.569897} at Lags [1]
            ARCH: {0.162344} at Lags [1]
        Leverage: {-0.162344} at Lags [1]