各位能不能帮我看一下下面的蒙特卡洛模拟啊，结果beta1hat竟然全是缺失值，而beta2hat却是正常的
clear
set more off
capt prog drop mtcarlo
prog mtcarlo,rclass
version 12.0
syntax [,obs(integer 10)]
drop _all
set obs `obs'
gen x=10*_n
tempvar y
local beta1=2
local beta2=0.6
gen `y'=`beta1'+`beta2'*x+uniform()
reg `y' x
return scalar beta1hat=_b[_cons]
return scalar beta2hat=_b[x]
end
simulate beta1hat=r(betalhat) beta2hat=r(beta2hat),reps(1000):mtcarlo