[Documentation][Fix] Streamable example using RequiredArgConstructor

[cailliaud]

Example of Streamable using @RequiredArgConstructor(staticName = "of") won't generate a static "of" waiting a Streamable if the field is not final or at least with @lombok.NonNull.
Based on Lombok documentation : https://projectlombok.org/features/constructor

Without a static constructor "of" containing the Streamable it will throw an :

java.lang.ClassCastException: class java.util.ArrayList cannot be cast to class [...] Products

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[mp911de]

Thanks for your contribution. That was already fixed with #2391