correct is_nil @doc to have the same format as the other is_* functions. So it is consistent in the Kernel > Summary docs
Use a not confusing example for String.grapheme
Merge pull request #2828 from eksperimental/fixing

correct is_nil @doc + String.grapheme better example
fix link to bug reports
Merge pull request #2830 from eksperimental/patch-1

fix link to bug reports