FIX: don't send nil user.name for MS Teams (#131)

Because Teams rejects the request for having a JSON `null` where a string is expected.

lib/discourse_chat_integration/provider/teams/teams_provider.rb

@@ -32,7 +32,12 @@ module DiscourseChatIntegration::Provider::TeamsProvider
 
   def self.get_message(post)
     display_name = "@#{post.user.username}"
-    full_name = SiteSetting.enable_names ? post.user.name : ""
+    full_name =
+      if SiteSetting.enable_names && post.user.name.present?
+        post.user.name
+      else
+        ""
+      end
 
     topic = post.topic
 

spec/lib/discourse_chat_integration/provider/teams/teams_provider_spec.rb

@@ -25,6 +25,18 @@ RSpec.describe DiscourseChatIntegration::Provider::TeamsProvider do
       expect(stub1).to have_been_requested.once
     end
 
+    describe 'with nil user.name' do
+      before do
+        post.user.update!(name: nil)
+      end
+
+      it 'handles nil username correctly' do
+        message = described_class.get_message(post)
+        name = message[:sections].first[:facts].first[:name]
+        expect(name).to eq("")
+      end
+    end
+
   end
 
 end