IsNullOrEmpty(this IEnumerable) extension method in public API causes CS0121 ambiguity for consumers

[scholarrx-pelka]

Duende.IdentityServer.Extensions.IEnumerableExtensions exposes a public IsNullOrEmpty extension method on IEnumerable. This is a very common utility method name, and any consumer library that defines its own IsNullOrEmpty(this IEnumerable) (or references one from another package) gets CS0121: The call is ambiguous compilation errors whenever both namespaces are imported.

The using Duende.IdentityServer.Extensions directive can't simply be removed because it provides other essential extensions like IsAuthenticated() and GetSubjectId() on ClaimsPrincipal.

Suggested fix:
Consider making IsNullOrEmpty(this IEnumerable) (and similar generic utility extensions) internal rather than public. It's a general-purpose helper that doesn't need to be part of the IdentityServer public API surface. This would eliminate the ambiguity for consumers without any behavioral change to IdentityServer itself.
Alternatively, moving it to a separate opt-in namespace (e.g., Duende.IdentityServer.Extensions.Internal) would also prevent the collision while keeping it accessible if explicitly desired.

[damianh]

Hi @scholarrx-pelka . Fair ask. Don't think think that particular item should be on the public API going forward, so we'll internalize it. As that's a breaking API change, it'll be on next major version.