TYPO3.Flow

I have several packages, for each package I like to create a routing shortcut.
So that instead of using these urls

test.local/Myverylongpersonalname.Myproject/posts
test.local/Myverylongpersonalname.MyprojectTest/images

test.local/mm/posts
test.local/test/images

I prefer to shorten the routes by adding subroutes to the global Routes.yaml like this:

-
  name: 'Myverylongpersonalname Myproject'
  uriPattern: 'mm/<MMSubroutes>'
  defaults:
    '@package': 'Myverylongpersonalname.Myproject'
  subRoutes:
    MMSubroutes:
      package: Myverylongpersonalname.Myproject

Now I would expect that I can add uriPattern: '' as a fallback route in the Routes.yaml of Myverylongpersonalname.Myproject, but I get:

The URI pattern "mm/" of route "Myverylongpersonalname Myproject :: fallback" ends with a slash, which is not allowed. You can put the trailing slash in brackets to make it optional.