you have a naked call to ggplot() with no data= being set.
my guess is that you intended to pipe the above manipulations of bike_rides into it.
Note:
My advice would be to only do such a pipe for the most trivial of charts, or when there are no issues for you to debug or alter ; if you have any difficulty at all with achieving a desired plot, its far better to make a new data.frame with its own name (bike_rides_to_plot) and explicitly pass that to ggplot.