Why can meson find hunt-net but not hunt-proton in dependency resolution?

[YD via Digitalmars-d-learn]

Hi, I am trying to use Meson, and I did the followings to get dub 
packages:

   dub fetch hunt-net
   dub fetch hunt-proton
   dub build hunt-net
   dub build hunt-proton
when I have this line in my meson.build file:

   dependency('hunt-net', method: 'dub')

It works fine:

   Run-time dependency hunt-net found: YES 0.4.6

But when I change it to

   dependency('hunt-proton', method: 'dub')

It simply says:

   Run-time dependency hunt-proton found: NO
   ... ERROR: Dependency "hunt-proton" not found

And when I looked at meson-log.txt, I couldn't find any clue on 
why that happens:

    Determining dependency 'hunt-proton' with DUB executable 
'.../dlang/dmd-2.091.0/linux/bin64/dub'
    Run-time dependency hunt-proton found: NO

So I completely cannot figure out why hunt-net is resolvable but 
hunt-proton is not. Can anyone help me understand how meson 
resolves these dependencies? Thanks!