How can I specify that I want a additive decomposition on seas function? about seasonal HOT 1 OPEN

library(seasonal)
m <- seas(AirPassengers, transform.function = "none")
summary(m)
#> 
#> Call:
#> seas(x = AirPassengers, transform.function = "none")
#> 
#> Coefficients:
#>                   Estimate Std. Error z value Pr(>|z|)    
#> Constant          30.62077    4.60956   6.643 3.08e-11 ***
#> Leap Year         11.32104    3.43088   3.300 0.000968 ***
#> Weekday           -0.90361    0.17787  -5.080 3.77e-07 ***
#> Easter[1]          6.89372    1.80972   3.809 0.000139 ***
#> AR-Nonseasonal-01  0.81929    0.04903  16.709  < 2e-16 ***
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
#> 
#> SEATS adj.  ARIMA: (1 0 0)(0 1 0)  Obs.: 144  Transform: none
#> AICc: 993.4, BIC:  1010  QS (no seasonality in final):    0  
#> Box-Ljung (no autocorr.):  29.2   Shapiro (normality): 0.984