Fix null reference error when filtering providers by language pairs

[devin-ai-integration]

Summary

Fixes the "Value can't be null. Parameter source" error that occurs when configuring the Trados plugin with "Routing as Disabled" and selecting any provider.

Root cause: The ProviderSupportsPair method was calling .Any() on provider.Pairs and provider.Symmetric arrays without null checks. Some providers may have null values for these arrays, causing an ArgumentNullException when LINQ methods are called on them.

Fix: Added null checks before calling LINQ methods on these potentially null arrays.

Review & Testing Checklist for Human

• Build verification: This is a .NET Framework 4.6.2 project that requires Windows to build. Please verify the solution builds successfully.
• Reproduce and verify fix: In Trados, configure the Intento plugin → Select "Routing as Disabled" → Select a provider (e.g., DeepL v2 or Google Advanced) → Click OK. Verify no error appears.
• Regression test: Verify that providers with valid language pairs still filter correctly when language pairs are specified.
• Test smart routing: Verify that selecting a routing option (not "Disabled") still works as expected.

Notes

• The fix changes behavior when both Pairs and Symmetric are null: the method now returns false (provider doesn't support the pair) instead of throwing an exception. This should be the correct behavior as providers without language pair data shouldn't match any specific language pair filter.

Link to Devin run: https://app.devin.ai/sessions/285b1ea5427e4f9da6c5e25c65367475
Requested by: Vladimir Popinov (@Xapgkop4uk)

---

Note

Fixes a null reference error during provider filtering.

• Adds null checks in ProviderSupportsPair for provider.Pairs and provider.Symmetric before calling Any()
• No functional changes elsewhere aside from file newline

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[devin-ai-integration]

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