Sup-t bands are not calculated if a coefficient was omitted in the regression

[Constantino-Carreto-Romero]

When running the following example

use example31.dta, clear
xtevent y eta , panelvar(i) timevar(t) policyvar(z) window(-9 8) reghdfe
xteventplot, ytitle(coefficient)

we get the following error message. The error seems to happen in the supt code. It might be related to https://github.com/JMSLab/xtevent/pull/172/files

[jorpppp]

@jorpppp will look into this