Two alternative ways to what Pior shared: The Skin modifier. This has the advantage of forkingCurves with a 'SphereCapCurve' modifier (can be found online, but I can send it if you DM me)
Note that poly curves are not quite the same as poly lines - the latter is still a mesh, just one that is made up of edges and vertices without faces (Blender specialty if I'm not mistaken - invalid geometry in most other apps I know). If you however convert that line to a curve then you end up with a (drumroll) ... poly…