Error(s) in re-building vignettes:
  ...
--- re-building ‘compare.margins.Rmd’ using rmarkdown

Quitting from compare.margins.Rmd:15-25 [unnamed-chunk-1]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<error/rlang_error>
Error:
! There is no valid predictor variable. Please change the `variables` argument or supply an alternative data frame to the `newdata` argument.
---
Backtrace:
    ▆
 1. └─marginaleffects::comparisons(...)
 2.   └─marginaleffects:::add_variables(variables = variables, mfx = mfx)
 3.     └─marginaleffects:::get_predictors(variables, mfx)
 4.       └─marginaleffects (local) stop_zero(predictors)
 5.         └─marginaleffects:::stop_sprintf(msg)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Error: processing vignette 'compare.margins.Rmd' failed with diagnostics:
There is no valid predictor variable. Please change the `variables` argument or supply an alternative data frame to the `newdata` argument.
--- failed re-building ‘compare.margins.Rmd’

--- re-building ‘count.fit.Rmd’ using rmarkdown
--- finished re-building ‘count.fit.Rmd’

--- re-building ‘daign.Rmd’ using rmarkdown
--- finished re-building ‘daign.Rmd’

--- re-building ‘first.diff.fitted.Rmd’ using rmarkdown
--- finished re-building ‘first.diff.fitted.Rmd’

--- re-building ‘list.coef.Rmd’ using rmarkdown
--- finished re-building ‘list.coef.Rmd’

--- re-building ‘margins.dat.Rmd’ using rmarkdown
--- finished re-building ‘margins.dat.Rmd’

--- re-building ‘margins.dat.clogit.Rmd’ using rmarkdown
--- finished re-building ‘margins.dat.clogit.Rmd’

--- re-building ‘margins.des.Rmd’ using rmarkdown
--- finished re-building ‘margins.des.Rmd’

--- re-building ‘rubins.rule.Rmd’ using rmarkdown
--- finished re-building ‘rubins.rule.Rmd’

--- re-building ‘second.diff.fitted.Rmd’ using rmarkdown
--- finished re-building ‘second.diff.fitted.Rmd’

SUMMARY: processing the following file failed:
  ‘compare.margins.Rmd’

Error: Vignette re-building failed.
Execution halted