Error(s) in re-building vignettes:
  ...
--- re-building 'introduction.Rmd' using rmarkdown
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_histogram' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_set' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_modal' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_set' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_modal' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_set' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_modal' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_set' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_histogram' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
S3 method lookup found 'vec_ptype_abbr.symbolic_interval' on search path 
Quitting from lines 109-117 (introduction.Rmd) 
Error: processing vignette 'introduction.Rmd' failed with diagnostics:
Problem with `summarise()` input `ViolentCrimesPerPop_hist`.
x Input must be a vector, not NULL.
i Input `ViolentCrimesPerPop_hist` is `sym.histogram(...)`.
i The error occured in group 1: state = 1.
--- failed re-building 'introduction.Rmd'

SUMMARY: processing the following file failed:
  'introduction.Rmd'

Error: Vignette re-building failed.
Execution halted