Add tests

app/models/command/go_to_card.rb

@@ -1,7 +1,7 @@
 class Command::GoToCard < Command
   store_accessor :data, :card_id
 
-  validates_presence_of :card_id
+  validates_presence_of :card
 
   def title
     "Visit card '#{card.title}'"

app/models/command/go_to_user.rb

@@ -1,7 +1,7 @@
 class Command::GoToUser < Command
   store_accessor :data, :user_id
 
-  validates_presence_of :user_id
+  validates_presence_of :user
 
   def title
     "View profile of '#{user.name}'"
@@ -13,6 +13,6 @@ class Command::GoToUser < Command
 
   private
     def user
-      User.find(user_id)
+      User.find_by_id(user_id)
     end
 end

app/models/command/parser/context.rb

@@ -22,7 +22,7 @@ class Command::Parser::Context
     attr_reader :controller, :action, :params
 
     def extract_url_components(url)
-      uri = URI.parse(url)
+      uri = URI.parse(url || "")
       route = Rails.application.routes.recognize_path(uri.path)
       @controller = route[:controller]
       @action = route[:action]