This code is basically copied from stats:::simulate.lm.
set_seed(seed = NULL)The integer vector containing the random number generate state will be returned, in order to call this function with this input to reproduce the obtained simulation results.
an object specifying if and how the random number generator
should be initialized ("seeded"). Either NULL (default) or an
integer that will be used in a call to set.seed() before
simulating the response vectors. If set, the value is saved as the
seed slot of the returned object. The default, NULL will
not change the random generator state.