Open Remote Desktop error

**Describe the bug**
In Visual Studio 2026, the AWS Explorer "Open Remote Desktop" action fails for some EC2 instances with the error:

`Error opening remote desktop: Nullable object must have a value.`

The same EC2 instances can be accessed successfully:
- through manual RDP
- through the same AWS Toolkit functionality in Visual Studio 2022

This indicates that the EC2 instances, credentials, and RDP connectivity are working correctly, and that the issue appears to be specific to AWS Toolkit behavior in Visual Studio 2026 for certain instances.

**To Reproduce**
1. Open Visual Studio 2026
2. Open AWS Explorer / AWS Toolkit
3. Navigate to EC2 instances
4. Right-click a Windows EC2 instance
5. Click **Open Remote Desktop**
6. For some instances, the following error appears:
`Error opening remote desktop: Nullable object must have a value.`

**Expected behavior**
"Open Remote Desktop" should open the RDP connection for all reachable EC2 Windows instances, the same way it does in Visual Studio 2022.

**Screenshots**
Screenshot of the error dialog is attached.

**Toolkit Logs**
Toolkit logs can be provided if needed. At the moment, the user-facing dialog only shows:
`Error opening remote desktop: Nullable object must have a value.`

**Development System (please complete the following information):**
- Windows Version: Windows 11 multpile builds
- Visual Studio Version: Visual Studio 2026 Community and Professional
- AWS Toolkit for Visual Studio Version: 1.90.0.0

**Additional context**
Additional observations:
- The issue occurs in both Visual Studio 2026 Community and Professional editions.
- The same AWS account / credentials are being used.
- Manual RDP works for all affected instances.
- The same instances also work correctly through AWS Toolkit in Visual Studio 2022.
- Only some EC2 instances fail in Visual Studio 2026; others open normally.

Possible relevance:
- The problem does not appear to be related to network connectivity, security groups, or RDP availability.
- The issue seems limited to how the toolkit constructs or opens the RDP session for certain EC2 instances.

Start by reproducing the Open Remote Desktop failure in Visual Studio 2026 with an affected EC2 instance, then compare it with the same instance in Visual Studio 2022. Collect the AWS Toolkit logs and identify which instance data or RDP-session step produces the nullable-value error; done means affected reachable Windows instances open successfully like they do in Visual Studio 2022.

Written by the indexing model from the issue text.