isErrorPage() check in RestoreViewPhase fails when thrown exception has a null message

[BalusC]

#5528

[BalusC]

Note: RequestMap#containsKey() doesn't work for 2 reasons:

1. Tomcat doesn't set request attribute at all, even not with a null value. Neither Servlet nor Faces spec are sufficiently explicit to blame Tomcat on this.
2. Mojarra's RequestMap impl doesn't check for attribute name but for attribute value (and this bug is apparently present in many other scope Map implementations -- this needs to be addressed via separate issue [Scope]Map#containsKey() doesn't check if key is present but only if value is non-null #5530

[mnriem]

Are there any tests that validate all the (new) code paths?

[BalusC]

Nope not yet.