Fix: sentry issue for slack incoming files check (#4656)

Interpreter error for nil. any? added nil. present?

Fixes: https://sentry.io/share/issue/48c10d26490f4bdaab78c82244fcea98/

spec/lib/integrations/slack/incoming_message_builder_spec.rb

@@ -61,6 +61,15 @@ describe Integrations::Slack::IncomingMessageBuilder do
         expect(conversation.messages.count).to eql(messages_count)
       end
 
+      it 'does not create message for invalid event type and event files is not present' do
+        messages_count = conversation.messages.count
+        message_with_attachments[:event][:files] = nil
+        builder = described_class.new(message_with_attachments)
+        allow(builder).to receive(:sender).and_return(nil)
+        builder.perform
+        expect(conversation.messages.count).to eql(messages_count)
+      end
+
       it 'saves attachment if params files present' do
         expect(hook).not_to eq nil
         messages_count = conversation.messages.count