Allow geometry nodes to take curves or meshes

I often use "curves" (read: collections of line segments which are technically curve objects) as instance targets. Sometimes I want to use the mirror modifier first. (Partly "because normals", but also because mirroring then instancing isn't the same as instancing then mirroring, if the instance isn't symmetrical.)

The problem is that curves can't be mirrored. (Why?) Fortunately, "Curve to Mesh" seems to not actually care if you feed it a mesh, except for making an annoying warning appear in the modifiers panel.

I would like a way to be able to create a node setup that can accept either a curve or a mesh. (Maybe just make "Curve to Mesh" accept a mesh as a no-op without the relatively meaningless warning?)