fix(cdk/scrolling): expand type for "cdkVirtualForOf" input to work with strict null checks #17421
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…ith strict null checks Currently the `cdkVirtualForOf` input accepts `null` or `undefined` as valid values. Although when using strict template input type checking (which will be supported by `ngtsc`), passing `null` or `undefined` with strict null checks enabled causes a type check failure because the type definition of the input becomes too strict with "--strictNullChecks" enabled. For extra content: by default if strict null checks are not enabled, `null` or `undefined` are assignable to _every_ type. The current type definiton of the `cdkVirtualForOf` input is incorrectly making the assumption that `null` or `undefined` are always assignable. The type of the input needs to be expanded to explicitly accept `null` or `undefined` to behave consistently regardless of the `strictNullChecks` flag. A common scenario where this breaks is the use of `cdkVirtualFor` in combination with the async pipe from `@angular/common`. This is because the async pipe returns `null` until a value has been emitted. This means that with strict null checks, the type checking will fail because `null` is not allowed. This is similar to what we did for `ngFor` in framework: angular/angular@c1bb886 Fixes angular#17411
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mmalerba
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Currently the
cdkVirtualForOfinput acceptsnullorundefinedas valid values. Althoughwhen using strict template input type checking (which will be supported by
ngtsc), passingnullorundefinedcauses a type check failure because the type definition of the input becomestoo explicit with "--strictNullChecks" enabled.
For extra content: by default if strict null checks are not enabled,
nullorundefinedare assignable to every type. The current type definiton of the
cdkVirtualForOfinputis incorrectly making the assumption that
nullorundefinedare always assignable.The type of the input needs to be expanded to explicitly accept
nullorundefinedto behave consistently regardless of thestrictNullChecksflag.This is similar to what we did for
ngForin framework: angular/angular@c1bb886Fixes #17411