feature engineering - dealing with conditional numeric variable

Let us say I have a dataset with 2 columns X1 and X2. X1 is dichotomous and has 2 level yes and no. X2 is numeric and is only completed when X1 = yes. Is it possible to keep the numeric column X2 as numeric? Could one impute the median of X2 for X1 = no or some other arbitrary constant? Thanks!

Let $$X1 = 1$$ if "yes" and $$0$$ if "no". Then, you can impute the value $$X2 = 0$$ for the units of observation having $$X1=0$$, and include in your regression the interaction term $$(X1\cdot X2)$$ instead of $$X2$$, so that the effect of $$X2$$ is conditional on $$X1 = 1$$.