R语言中plot.gam为什么画不了阶梯性质的参量

plot(gam3,se＝T,col＝''blue'')
Warning message:
In gplot.default(x = c("male", "female", "femal''
The "x" component of "partial for sex" has class "character"; no gplot() methods available这是哪出问题了呢？