Blueprint library compiles ok. but fails to save

"Can’t save …/…/…/…/UnrealProjects/ahsanGameArchive/Content/ahsanAssets/blueprintLib/widgetLib.uasset: Graph is linked to private object(s) in an external package.
External Object(s):

Try to find the chain of references to that object (may take some time)?"

press ok then shows this:

"The asset ‘/Game/ahsanAssets/blueprintLib/widgetLib’ (widgetLib.uasset) failed to save.

Cancel: Stop saving all assets and return to the editor.
Retry: Attempt to save the asset again.
Continue: Skip saving this asset only."

here is a video:

i have tried several time to create the blueprint library.
it works ok at the beginning .
but later whenever i open the project, it always fails to save it.

and after some investigating it looks like that using “getGameMode()” always adding a 2nd parameter of type “world context” and that is the culprit.
here i have shown it:

any idea,how to remove this “world context” or what to input in that pin?link text

anyone from epic?