tumblr: don't fail when api key isn't configured.

app/logical/sources/strategies/tumblr.rb

@@ -8,6 +8,10 @@ module Sources::Strategies
     IMAGE = %r!\Ahttps?://#{DOMAIN}/(?<dir>#{MD5}/)?#{FILENAME}_#{SIZES}\.#{EXT}\z!i
     POST = %r!\Ahttps?://(?<blog_name>[^.]+)\.tumblr\.com/(?:post|image)/(?<post_id>\d+)!i
 
+    def self.enabled?
+      Danbooru.config.tumblr_consumer_key.present?
+    end
+
     def self.match?(*urls)
       urls.compact.any? do |url|
         blog_name, post_id = parse_info_from_url(url)
@@ -174,7 +178,7 @@ module Sources::Strategies
     memoize :inline_images
 
     def client
-      raise NotImplementedError.new("Tumblr support is not available (API key not configured).") if Danbooru.config.tumblr_consumer_key.nil?
+      return {} unless self.class.enabled?
 
       TumblrApiClient.new(Danbooru.config.tumblr_consumer_key)
     end

test/unit/sources/tumblr_test.rb

@@ -3,8 +3,7 @@ require 'test_helper'
 module Sources
   class TumblrTest < ActiveSupport::TestCase
     def setup
-      super
-      skip "Tumblr key is not configured" unless Danbooru.config.tumblr_consumer_key
+      skip "Tumblr key is not configured" unless Sources::Strategies::Tumblr.enabled?
     end
 
     context "The source for a 'http://*.tumblr.com/post/*' photo post with a single image" do