Rails will always raise an ActiveRecord::RecordNotFound exception when you use the find method. The find_by_* methods, however, return nil when no record is found.
The ActiveRecord documentation tells us:
RecordNotFound – No record responded to the find method. Either the
row with the given ID doesn’t exist or the row didn’t meet the
additional restrictions. Some find calls do not raise this exception
to signal nothing was found, please check its documentation for
further details.
If you’d like to return nil when records cannot be found, simply handle the exception as follows:
begin
my_record = Record.find params[:id]
rescue ActiveRecord::RecordNotFound => e
my_record = nil
end