* Make keystore return `None` when a key doesn't exist

* Fixes

* More fixes

* Update comment

* Update primitives/keystore/src/lib.rs

Co-authored-by: André Silva <[email protected]>

* Update client/keystore/src/local.rs

Co-authored-by: André Silva <[email protected]>

* Address comments

* Update client/keystore/src/local.rs

Co-authored-by: André Silva <[email protected]>

Co-authored-by: André Silva <[email protected]>