If you downloaded the new Base library for V4.1.1.1, do not
install this pathch since it is already a part of the Base library.
If you are running the latest version of V4.1 and have not
installed the new Base library, doing so will fix this problem as
well as others.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Fix to IsKeyed of Base$KeyedCollection
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If you downloaded the new Base library for V4.1.1.1, do not
install this pathch since it is already a part of the Base library.
If you are running the latest version of V4.1 and have not
installed the new Base library, doing so will fix this problem as
well as others.