Properly migrate users with usernames like "." or "..".

app/models/namespace.rb

@@ -66,9 +66,13 @@ class Namespace < ActiveRecord::Base
       path.gsub!(/\.+\z/,             "")
       path.gsub!(/[^a-zA-Z0-9_\-\.]/, "")
 
+      # Users with the great usernames of "." or ".." would end up with a blank username.
+      # Work around that by setting their username to "blank", followed by a counter. 
+      path = "blank" if path.blank?
+
       counter = 0
       base = path
-      while Namespace.by_path(path).present?
+      while Namespace.find_by_path_or_name(path)
         counter += 1
         path = "#{base}#{counter}"
       end

db/migrate/20150324133047_remove_periods_at_ends_of_usernames.rb

@@ -15,6 +15,10 @@ class RemovePeriodsAtEndsOfUsernames < ActiveRecord::Migration
         path.gsub!(/\.+\z/,             "")
         path.gsub!(/[^a-zA-Z0-9_\-\.]/, "")
 
+        # Users with the great usernames of "." or ".." would end up with a blank username.
+        # Work around that by setting their username to "blank", followed by a counter.
+        path = "blank" if path.blank?
+
         counter = 0
         base = path
         while Namespace.find_by_path_or_name(path)