Fix little typo is JsPath.scala

Just a little typo in `readNullable` documentation.
Merge pull request #1488 from studiodev/patch-1

Fix little typo is JsPath.scala
Do not allow setting null cookie values. null values are typically allowed in Java maps so it is confusing that they are not allowed here, but no error is given to indicate that
Merge pull request #1495 from benmccann/cookie-baker-encoding-fix

Throw a better exception when user tries to set null cookie value