docs: def _storeFromUsername(store, username):
      """
      Find the user store of the user with username C{store}
  
      @param store: site-store
      @type store: L{axiom.store.Store}
  
      @param username: the name a user signed up with
      @type username: C{unicode}
  
      @rtype: L{axiom.store.Store} or C{None}
      """
      lm = store.findUnique(
              userbase.LoginMethod,
              attributes.AND(
                  userbase.LoginMethod.localpart == username,
                  userbase.LoginMethod.internal == True),
              default=None)
      if lm is not None:
          return lm.account.avatars.open()