Fix import of snippets with `award_emoji`

Snippets having `award_emoji` failed being imported.
It happened because `award_emoji` model validation failed.
It also prevented other snippets being imported as the process silently
failed mid-iteration.

app/models/award_emoji.rb

@@ -6,11 +6,14 @@ class AwardEmoji < ApplicationRecord
 
   include Participable
   include GhostUser
+  include Importable
 
   belongs_to :awardable, polymorphic: true # rubocop:disable Cop/PolymorphicAssociations
   belongs_to :user
 
-  validates :awardable, :user, presence: true
+  validates :user, presence: true
+  validates :awardable, presence: true, unless: [:importing?]
+
   validates :name, presence: true, inclusion: { in: Gitlab::Emoji.emojis_names }
   validates :name, uniqueness: { scope: [:user, :awardable_type, :awardable_id] }, unless: :ghost_user?
 

spec/fixtures/lib/gitlab/import_export/complex/project.json

@@ -2260,7 +2260,41 @@
       ]
     }
   ],
-  "snippets": [],
+  "snippets": [
+    {
+      "id": 1,
+      "title": "Test snippet title",
+      "content": "x = 1",
+      "author_id": 1,
+      "project_id": 1,
+      "created_at": "2019-11-05T15:06:06.579Z",
+      "updated_at": "2019-11-05T15:06:06.579Z",
+      "file_name": "",
+      "visibility_level": 20,
+      "description": "Test snippet description",
+      "award_emoji": [
+        {
+          "id": 1,
+          "name": "thumbsup",
+          "user_id": 1,
+          "awardable_type": "Snippet",
+	  "awardable_id": 1,
+          "created_at": "2019-11-05T15:37:21.287Z",
+          "updated_at": "2019-11-05T15:37:21.287Z"
+        },
+        {
+          "id": 2,
+          "name": "coffee",
+          "user_id": 1,
+          "awardable_type": "Snippet",
+	  "awardable_id": 1,
+          "created_at": "2019-11-05T15:37:24.645Z",
+          "updated_at": "2019-11-05T15:37:24.645Z"
+        }
+      ],
+      "notes": []
+    }
+  ],
   "releases": [],
   "project_members": [
     {

spec/lib/gitlab/import_export/project_tree_restorer_spec.rb

@@ -210,6 +210,17 @@ describe Gitlab::ImportExport::ProjectTreeRestorer do
         expect(@project.project_badges.count).to eq(2)
       end
 
+      it 'has snippets' do
+        expect(@project.snippets.count).to eq(1)
+      end
+
+      it 'has award emoji for a snippet' do
+        award_emoji = @project.snippets.first.award_emoji
+
+        expect(award_emoji.count).to eq(2)
+        expect(award_emoji.map(&:name)).to match_array(%w[thumbsup coffee])
+      end
+
       it 'restores the correct service' do
         expect(CustomIssueTrackerService.first).not_to be_nil
       end