Return null if active IVsHierarchy is null
Return null if active IVsHierarchy is null

This can happen when the current project is unloaded, for example.

kzu/clide,clariuslabs/clide,kzu/clide,clariuslabs/clide,kzu/clide,clariuslabs/clide,tondat/clide,tondat/clide,tondat/clide