fix: Resolve name only if assignee exists during unassignment (#1649)

spec/controllers/api/v1/accounts/conversations/assignments_controller_spec.rb

@@ -29,5 +29,25 @@ RSpec.describe 'Conversation Assignment API', type: :request do
         expect(conversation.reload.assignee).to eq(agent)
       end
     end
+
+    context 'when conversation already has an assignee' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+
+      before do
+        conversation.update!(assignee: agent)
+      end
+
+      it 'unassigns a user from the conversation' do
+        params = { assignee_id: 0 }
+        post api_v1_account_conversation_assignments_url(account_id: account.id, conversation_id: conversation.display_id),
+             params: params,
+             headers: agent.create_new_auth_token,
+             as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(conversation.reload.assignee).to eq(nil)
+        expect(conversation.messages.last.content).to eq("Conversation unassigned by #{agent.name}")
+      end
+    end
   end
 end