Fix inconsistent return type

app/controllers/projects/mattermosts_controller.rb

@@ -34,7 +34,10 @@ class Projects::MattermostsController < Projects::ApplicationController
   end
 
   def teams
-    @teams ||= @service.list_teams(current_user)
+    @teams ||= begin
+                 teams, error_message = @service.list_teams(current_user)
+                 error_message ? error_message : teams
+               end
   end
 
   def service

app/models/project_services/mattermost_slash_commands_service.rb

@@ -30,8 +30,8 @@ class MattermostSlashCommandsService < ChatSlashCommandsService
 
   def list_teams(user)
     Mattermost::Team.new(user).all
-  rescue Mattermost::Error => e
-    [[], e.message]
+  rescue Mattermost::Error
+    []
   end
 
   private

lib/mattermost/client.rb

@@ -27,12 +27,12 @@ module Mattermost
     end
 
     def json_response(response)
-      json_response = JSON.parse(response.body)
-
       unless response.success?
         raise Mattermost::ClientError.new(json_response['message'] || 'Undefined error')
       end
 
+      json_response = JSON.parse(response.body)
+
       json_response
     rescue JSON::JSONError
       raise Mattermost::ClientError.new('Cannot parse response')

spec/controllers/projects/mattermosts_controller_spec.rb

@@ -13,13 +13,13 @@ describe Projects::MattermostsController do
     before do
       allow_any_instance_of(MattermostSlashCommandsService).
         to receive(:list_teams).and_return([])
+    end
 
+    it 'accepts the request' do
       get(:new,
           namespace_id: project.namespace.to_param,
           project_id: project.to_param)
-    end
 
-    it 'accepts the request' do
       expect(response).to have_http_status(200)
     end
   end

spec/models/project_services/mattermost_slash_commands_service_spec.rb

@@ -113,10 +113,7 @@ describe MattermostSlashCommandsService, :models do
         end
 
         it 'shows error messages' do
-          teams, message = subject
-
-          expect(teams).to be_empty
-          expect(message).to eq('Failed to get team list.')
+          expect(subject).to eq([])
         end
       end
     end