Address MR review comments

lib/gitlab/ci/runner_releases.rb

@@ -58,13 +58,22 @@ def cache_key
       end
 
       def backoff_active?
-        return unless @backoff_expire_time
+        return false unless @backoff_expire_time
 
         Time.now.utc < @backoff_expire_time
       end
 
       def extract_releases(response)
-        response.parsed_response.map { |release| parse_runner_release(release) }.sort!
+        return unless response.parsed_response.is_a?(Array)
+
+        releases = response.parsed_response
+          .map { |release| parse_runner_release(release) }
+          .select(&:valid?)
+          .sort!
+
+        return if releases.empty? && response.parsed_response.present?
+
+        releases
       end
 
       def parse_runner_release(release)

spec/lib/gitlab/ci/runner_releases_spec.rb

@@ -112,6 +112,18 @@ def releases
 
       it_behaves_like 'requests that follow cache status', 1.day
     end
+
+    context 'when response contains unexpected input type' do
+      let(:response) { 'error' }
+
+      it { expect(releases).to be_nil }
+    end
+
+    context 'when response contains unexpected input array' do
+      let(:response) { ['error'] }
+
+      it { expect(releases).to be_nil }
+    end
   end
 
   describe '#expired?', :use_clean_rails_memory_store_caching do