cryptic error in `prop.test` explainer with 3 or more proportions

[davharris]

I tried adding a check for it in the code, but I don't think I understand the big picture well enough to capture the error effectively.

> prop.test(c(11, 10, 4), c(12, 12, 12)) %>% explain()
Quitting from lines 124-128 () 

## Error in if (x$p.value < 1 - attr(x$conf.int, "conf")) {: argument is of length zero

## Warning: NAs introduced by coercion

## Error in if (x$p.value < 1 - attr(x$conf.int, "conf")) "reject" else "do not reject": argument is of length zero

Warning message:
In prop.test(c(11, 10, 4), c(12, 12, 12)) :
  Chi-squared approximation may be incorrect