[BUG] summarise() returns an error

[nathaneastwood]

In {dplyr}:

> mtcars %>% summarise()
data frame with 0 columns and 1 row
> mtcars %>% group_by(am, cyl) %>% summarise()
`summarise()` regrouping output by 'am' (override with `.groups` argument)
# A tibble: 6 x 2
# Groups:   am [2]
     am   cyl
  <dbl> <dbl>
1     0     4
2     0     6
3     0     8
4     1     4
5     1     6
6     1     8

In {poorman}:

r$> mtcars %>% summarise()                                                                                                                                       
NULL

r$> mtcars %>% group_by(am, cyl) %>% summarise()                                                                                                                 
Error in data.frame(..., check.names = FALSE) : 
  arguments imply differing number of rows: 1, 0